Base Dressing Fertilisers & Bonsai

Feb 12, 2025 | Bonsai Tree Care

Base Dressing Fertilisers & Bonsai

Way back when I started bonsai in those halcyon days just before the internet ruined most everything, after I had exhausted my local library, I stumbled into a local bonsai club. This had what might kindly be called a parochial attitude to our hobby. Very traditional in approach, were it not for the lack of impressive produce one could be forgiven for thinking it was a meeting of allotment holders. In fact many folk there were indeed allotment holders, me included eventually.

I remember vividly how entrenched ideas were and anything new, especially from a whipper-snapper like me (yes I was young once) caused much furrowing of collective brows. The debate around Akadama vs John Innes and grit eventually became quite aggravated but the one I loved most was the conflict over chemical vs organic fertilisers.

Back then gardeners had a lot less choice and with an almost complete lack of bonsai tree specific fertilisers our options were minimal. I remember that chicken manure in a dried pellet form was just becoming widely available at the fledgling ‘big sheds’ like the new B&Q mega stores that were popping up all over. Fish/blood & bone was another traditional “organic“, nasty stuff! On the other side of the equation there was Phostrogen, Miracle-gro and Tomorite.

We did have one enlightened individual that introduced me to the use of Rapeseed as fertiliser. This could easily be turned into ‘tea’, pellets or even applied in its raw state. I had seen it’s use in Japanese books but at the time no commercially prepared products were available here and besides I would NOT have been able to afford them.

I instantly understood the value of organics as fertiliser. Not only did they provide nutrients to the tree but they also supported invaluable bacterial and fungal activity within the soil and somehow it made perfect sense to me. Today I use 99% organic fertilisers across my garden wether for bonsai, my wife’s flower garden or veg’ and fruit growing.

I have to say that within our genteel pass-time still those two subjects are contentious. I don’t see the need for so much tribal conflict though. At the end of the day, if it works for you keep at it…. a la salud! Still, it’s in our nature to be tribal and fight and if that’s your thing ‘have at it‘.

At the end of the day it matters little what soil or fertilisers you use for growing bonsai. What matters is how you manage the whole process. Everyone seems to want a free draining ‘soil’ for bonsai but I have had a great deal of success using straight garden soil. One lovely old fellow I met had used nothing else for 30 years and when I got the chance to buy his collection I kept most of it personally because the trees were so good.

The soil bonsai are in matters less than how we manage it. Using sandy garden soil certainly reduces the need for watering in summer but then it does need careful management in a soggy British winter. Fertilisers are the same, included within an intricately structured care regimen most will supply what the plant needs. However….

Managing a bonsai tree is always going to be complicated if we want it to do more than just survive. There are infinite variables to consider and these constantly change. Maintaining optimum growing conditions all the time is impossible but we need to do the best we can. Fortunately most plants used for bonsai are tough and tolerant so that helps us. For instance if a tree gets a bit too much sun during the height of summer it might get a bit scorched but it’ll live.

Ultimately it’s a lot easier to use a modern bonsai soil mix and purpose designed fertilisers than it is to craft our skill of managing a plant and all the complications that come with it. Now I firmly believe refining our horticultural skill to that level has great benefit but it’s not for everyone and not everyone has the prerequisite skills to achieve success. So it’s good that nowadays we have lots of great products to help us out, make our bonsai better and free us up from the slavish devotions of fanatical horticultural discipline.

I came here to introduce the concept of ‘Base Dressing’. That is the process of adding a nutrient rich substance, in our case a prepared fertiliser to soil. This is a common practice in gardening. As I sit here tapping away at my keyboard fanatical gardeners and allotment holders across the country are busy digging in mountains of festering animal poo before the new season gets under way. This is a time honoured ritual and ensures a good crop from a hard worked garden.

So why don’t we use base dressing in bonsai cultivation? I’m sure some folk do but I was always lead to believe that fertiliser and a newly repotted tree should be treated in much the same way as a bathtub full of water and a toaster. As little contact as possible for the good of all concerned but why?

Last year we put out a little booklet containing my thoughts on fertilisers and bonsai cultivation. If you have read it you will know how fertilisers work and how they release nutrients, you will also know the golden rule, never fertilise a plant that’s not actively growing. There’s a lot of that information contained in the multitudes of old posts here if you search the archives, lots more is contained within the articles posted on our web site. I will try to get the booklet text up soon.

Fertilisers release nutrients in different ways. Refined chemicals tend to be a bit like an intravenous injection, they quickly dilute in water and are rapidly absorbed into the plant, often within minutes or a few hours. Organics however rely on fungi and bacteria to break them down and release the nutrients. Some poorly suited organics do both.

I have talked endlessly about reverse osmosis, what is commonly called fertiliser burn. This is when too much nutrient around the roots causes water and nutrients to be drawn out of the plant causing its water column to collapse. This typically manifests as wilting initially followed by browning or dropping leaves. In time twigs and branches can be lost and entire plants can quickly die. To see a similar result try sprinkling cucumber slices in a bowl with salt.

So if the golden rule is don’t feed a tree that’s not actively growing and knowing fertilisers can cause reverse osmosis why would we add fertiliser to the soil of a bonsai tree when repotting, especially as most trees are repotted at the end of the dormant season and therefore not actively growing?

First up bear in mind that a bonsai tree grows (very slowly) in a small amount of soil. Unlike your hanging baskets and grow bags that get composted at the end of the season bonsai trees need to be healthy for many decades. We have a very unique set of circumstances and so the horticulture used for bonsai is entirely different from that used for almost any other container cultivation.

An actively growing bonsai tree can be expected to strip out most of a soils inherent nutrient within a couple of weeks and our constant watering will do little to help. A growing plant needs tiny amounts of nutrient constantly therefore we need to have a drip, drip approach to fertiliser application and that’s easy to set up with organics. It’s not so easy with chemicals, it can be done but it needs constant monitoring.

There are largely two types of folk in bonsai. Those who are in a hurry, typically newbies, who believe they can push their trees to go faster by the copious and repeated application of fertilisers. Secondly we have those who don’t feed much at all, possibly because they believe it’s all ‘snake oil’ or commercial hokum. I once met a guy who only used water from his koi pond believing the nutrients (which grew copious amounts of blanket weed) were all the bonsai needed. After decades this particular theory was entirely disproven after I saw his poorly looking tree collection.

On the other hand I remember when I was landscape gardening I got hold of a large volume of lawn fertiliser/moss killer/weeder. One of those fucking wonder products that turn your crusty old mud patch full of divots and dog piss patches into a snooker table without any effort whatsoever. Used correctly that might be the case (not) however I gave a sack to my dad. Rather than read the instructions he dumped the whole 25kg onto his fairly big lawn in one go. Ten days later the grass had tuned to nasty black slime.

Getting it right with fertilisers is important whichever way you decide to go and base dressing is an important part of that. Modern bonsai soils are almost entirely devoid of nutrient, they are largely made up of processed aggregates which either have no inherent nutrients or the nutrients were destroyed in processing, firing, washing etc’. We like it that way because we gain control. It’s a bit like when I make cornbread. If I don’t get the preparation right when putting everything together what comes out of the oven won’t be right. In that example it’s no good blaming the oven.

Here at KB we spend more time getting soil right than anyone in the country, it’s always been my passion and today we move close to a thousand kilos of mix every day. This goes to folk growing everything from bonsai masterpieces to plants that eat animals and those growing plants in their wardrobes. We know it’s right so long as it’s used right.

What base dressing does is to light up our inert soil mixes. Unlike normal fertilisers those designed for base dressing in bonsai have been carefully crafted to bring maximum vitality and life to soil without excess NPK which can, as mentioned, cause damaging reverse osmosis. Those nutrients are not required in volume during the crucial period after re-potting. However micro nutrients are, particularly as new fine feeder roots emerge and need those nutrients to create new cells and tissue.

Base dressing also fires up the flora and fauna so crucial to building a dynamic ecosystem within our little pots. Continuing with my cooking analogy base dressing products for bonsai put the heat in the oven. No matter how careful we are in creating a good bonsai soil mix, without the fungi and bacteria required we’ll not be ‘cooking’ and nobody wants to eat raw cornbread batter.

I think part of the problem is where a base dressing product is referred to as a fertiliser which causes the confusion about not feeding newly repotted trees. Over the past several years I have been using base dressing products for all my repotted trees. It’s something I now consider essential at every repot across all the species I keep including deciduous and coniferous varieties. We now carry two primary products for base dressing and my extensive use of both has moved my bonsai forward significantly.

Green Dream™ Soil Source Natural Micro-Biological Soil Additive

There is an extensive explanation of this products use and benefits on the product description page of our web site (click text above for link).

Green Dream™ Soil Source Natural Micro-Biological Soil Additive

Green Dream™ Soil Source is a product that we have developed over the last few years. This is a groundbreaking microbial soil additive product unlike anything else available that is simply added to your chosen soil mix or growing media at repotting time. The product, which on the face of it looks like our Green Dream Original product (small dry crumbs), is packed with beneficial micro-organisms like Trichoderma harzianum which are very well documented as being supremely beneficial to the cultivation of plants and the development of roots in horticulture.

Over several years we added this unique new product to well in excess of four hundred repotted plants at various stages of bonsai development. The results were surprising to say the least. Every plant has thrived, regardless of the growing media or species involved, every plant started growing much earlier than normal and much more strongly and once good growth was underway we noticed a significant improvement in the plants uptake of nutrients from fertilizers with improved growth rate, foliage colour and robust appearance. Over the summer period we also saw a dramatic reduction in problems with pest and disease reducing our use of chemical sprays by over 75%.

Biogold Classic Motohi Premium Organic Bonsai Base Dressing Fertiliser

The original fertiliser from the renowned Japanese BioGold range. There is an extensive explanation of this products use and benefits on the product description page of our web site (click text above for link).

Biogold Classic Motohi Premium Organic Bonsai Base Dressing Fertiliser

“The origins of Bio Gold date back to around 1970. Toshio Tsubaki, a doctor of agriculture who was heavily involved in the product’s development, had been researching microorganisms related to plant growth for over 10 years. However, the discovery of effective microorganisms did not go as expected, and during the days of struggle, he met Kazuo Yamaguchi (then Professor Emeritus at Ibaraki University), an authority on applied microbiology, through a book.

From there, the two began joint research, and in 1983, they finally discovered the bacteria (microorganisms) that became the source of Bio Gold. It was a product that allowed plants and soil microorganisms to draw out each other’s strengths, improving the soil environment and promoting strong plant growth. Bio Gold was developed to take advantage of the functions of these microorganisms and make it easy for anyone to use.

The natural activator that would become Bio Gold was born. This product was later improved and evolved into “Classic Base Fertilizer” and “Bio Gold Vital.”  First released 1986 and in continual production ever since.

This is a solid, organic, slow release base dressing fertiliser. Ideal in autumn and at the time of repotting all bonsai. It creates and nourishes vital roots which are very important for plant growth. Because it is carefully matured over time, using a unique fermentation method, there is no need to worry about damaging plant roots.

Besides the above it’s also possible to add products to your soil mix that are not referred to as fertilisers but contain high levels of nutrient that takes longer to release. These provide a base level of nutrition, often for several months. This is a very useful technique, particularly when dealing with poorly trees. My own personal favourite is….

Green Dream™ – Seaweed Meal – Soil Conditioner & Fertiliser

Green Dream™ – Seaweed Meal – Soil Conditioner & Fertiliser

100% pure sustainable dried British seaweed meal (ascophyllum nodosum). A natural organic plant feed and soil conditioner packed with nutrients. Safely encourages and sustains growth and vitality in all plants from seedlings to ancient trees. Improves pest resistance, soil bio-activity, fertility, water and nutrient holding capacity. Broad spectrum nutrients that are released to the plant slowly over a whole growing season.

To Sum Up…

Personally I highly recommend base dressing when repotting bonsai. It’s something I now do as a matter of course for all my trees. A good modern soil mix with organic base dressing coupled with the use of quality organic fertilisers throughout the growing season and careful watering is a combination that’s hard to beat.

When you grow bonsai in a crappy climate like the one we have to endure here in GB every little advantage must be sought out in order to get the best results and base dressing is an oft overlooked, proven and time honoured technique that needs to be universally adopted. Give base dressing a go this repotting season!

Graham Potter

Lime Sulphur – A Miracle Solution

Jan 29, 2025 | Bonsai Tree Care

Most people involved in bonsai for any period of time will likely be familiar with Lime Sulphur. It’s that grubby little bottle of stinky red stuff in the bottom of your tool bag that’s used to preserve and colour deadwood and dissolve little paintbrushes. Doing that particular chore is on nobody’s wish list. BUT did you know that little bottle contains a miracle solution that can significantly raise your bonsai game? Lime sulphur has a huge number of uses and solves a significant number of pernicious problems faced by growers. From pest control to fertiliser, Lime Sulphur is remarkable. So, please give me a few minutes and let’s learn something!

Lime Sulphur – A Miracle Solution – Eradicant, disinfectant & fertiliser! Who knew?

What is Lime Sulphur?

There are a lot of ‘old wives tales’ out there concerning Lime Sulphur. Forget all that, let’s take a look at the facts.

Lime Sulphur is a red liquid with a distinctive rotten egg smell that’s soluble in water. Lime sulphur is used primarily to control pests and disease in horticulture. It’s a saturated aqueous solution of calcium polysulphides, and its use is accepted and approved in organic cultivation in both the UK and EU. Lime sulphur is made by reacting together sulphur and lime in water.

Lime Sulphur is a red liquid with a distinctive rotten egg smell that’s soluble in water.

Lime sulphur is alkaline with a typical pH of 10.5-11.5 so it’s considered caustic or corrosive, to put that into perspective, it’s alkalinity is somewhere between milk of magnesia at pH10.5 and many household cleaners that have a pH between 11-13. It has to be handled very carefully due to fumes that are hazardous but beyond that it’s a fairly safe product to use.

A Fascinating History.

Lime sulphur is believed to be the earliest synthetic (man made) chemical used as a pesticide sometime around the 1840s in France to control grape vine powdery mildew, which had been introduced from the USA in 1845 and reduced wine production by 80%. In 1886 it was first used in California to control San Jose scale and peach leaf curl.

Today many chemicals have been banned, folk are discovering many of the old ways again. Old timers knew a thing or two!

Commencing around 1904, commercial suppliers began to manufacture lime sulphur; prior to that time, growers were expected to manufacture their own. By the 1920s essentially all commercial orchards in western countries were protected by regular spraying with lime sulphur. However by the 1940s, lime sulphur began to be replaced by synthetic fungicides which risked less damage to the crop’s foliage. With hindsight we know that was something of a mistake. Now many of those chemicals have been banned folk are discovering many of the old ways again. Lime sulphur is an effective, safe and sustainable product when used correctly and wisely.

Lime Sulphur – How It Works.

Lime Sulphur is an agent of eradication, a substance that destroys a parasitic organism or infection at the point of contact (i.e. not systemic) and has been used in horticulture for centuries due to its fungicidal and insecticidal properties. Lime Sulphur is highly effective against a range of pests and diseases, making it a valuable tool in the arsenal of growers.

Lime sulphur breaks down after it’s applied, releasing valuable plant nutrients. The sulphur dioxide is the main element that’s toxic to insects and fungi, and it eradicates them through direct contact or through fumigation which can work from a slight distance. In simple terms sulphur is absorbed by insects and it interferes with their ability to create energy, it also releases hydrogen sulphide gas (smells of rotten egg) which poisons them. It is toxic to insects and mites due to hydrogen sulphide formed through reaction of the polysulphide components with water and carbon dioxide, or put more simply, lime sulphur reacts with the atmosphere to produce hydrogen sulphide which poisons the pests.

A short time after application lime sulphur breaks down into it’s constituent parts of lime and sulphur. The hydrogen sulphide quickly dissipates and what’s left are two extremely valuable plant nutrients in the form of ……lime and sulphur. More on that later.

Lime Sulphur can be used in the UK and EU as a fungicide, insecticide and miticide. This includes organic crops. As covered in EU Regulations (EC) No 889/2008.

Is Lime Sulphur Safe to Use?

In a word…..no. However all manner of everyday products aren’t safe either but used correctly the dangers are minimal. There’s a tin of Brasso in the office, it’s great for cleaning metals but were I to drink it or pour it into my ear daily it’s almost certainly hazardous to my health. Same with bleach, fertilisers, fuels, glue and even some food products, my dad recons my home made hot sauce is extremely dangerous! We live in the age of overbearing ‘health & safety’ rules which might lead one to believe even being in the same building as a chemical could be injurious. We need to be sensible, take suitable precautions and all will be well.

If lime sulphur were 100% safe it would be useless. Taking simple precautions will ensure complete safety for the user whilst successfully achieving the desired result. It has to be handled very carefully due to fumes that are hazardous. But, Lime Sulphur is an extremely effective tool for pest and disease management and presents minimum risk to the user.

Lime Sulphur is safe to use but do take appropriate safety measures. 🙂

It is essential that you follow the proper safety precautions listed on the label when using Lime Sulphur, including wearing protective gloves, goggles, and a FFP3 type B filter mask. As part of its action, Lime Sulphur releases hydrogen sulphide gas which smells of rotten eggs and is hazardous to humans. So only use in well ventilated areas.

A few hours after application Lime Sulphur will be fully reacted and is no longer hazardous. It actually converts into plant-available nutrients (calcium and sulphur). As Lime Sulphur has a non-residual action, and is composed of simple chemicals, it can be used in organic growing and has no detrimental long term environmental impact.

Lime sulphur should be kept well away from the aquatic environment, children, animals and anything else you do not want to kill. When spraying always work outside and try to stand upwind to avoid being covered in overspray or breathing vapours. Spray yourself then walk in the house and the consequences may well be dire if your other half is home! Fortunately lime sulphur washes out of clothes easily but skin contamination may take a day or two to dissipate completely.

Whilst it feels redundant to point out the following I have seen folk do all of these things. Keep lime sulphur off your skin or it’ll smell for a couple of days which is both embarrassing and detrimental to marital harmony. Keep out of your eyes, splashes will sting like hell, irrigate with lots of clean water. Avoid exposure to fumes, these can sting eyes and should not be inhaled. Do not rinse used brushes in your tea or drink. Lime sulphur, being alkaline would react with stomach acid releasing that sulphur dioxide and could end in a Mr Creosote type scenario.

Lime sulphur reacts with strong acids. NEVER MIX WITH ANYTHING OTHER THAN CLEAN TAP WATER.

Due to its high sulphur content, Lime Sulphur has a strong odour but this quickly disperses. When using in glasshouses or covered areas, ensure adequate ventilation. Store in a cool dry place, away from heat and free from freezing. Keep sealed in it’s original container and secured away from unauthorised users, children, wildlife and pets. STORE AWAY FROM ACIDS.

Always source Lime Sulphur from a reputable supplier. Home made products are just too variable to be considered safe especially when treating expensive bonsai trees. Just don’t take the risk on a cheap bottle your mate whipped up in his backyard or you found on an auction site.

Good Lime sulphur can last for up to five years if stored properly in a quality container, but it’s best to use it within two years. Use diluted solutions immediately. An old, out of date or contaminated product may be suitable for painting onto bonsai deadwood but do not use for treating plant P&D (pest & disease).

So, enough of all this health and safety, what can Lime Sulphur actually do?

Pest and Disease Control with Lime Sulphur

Most bonsai folk will be familiar with the use of lime sulphur to winter wash. Winter washing is the process of spraying dormant leafless trees in late winter to eradicate fungi and pests that may be hiding in the bark and branches. These often emerge as the weather warms up and cause problems. However as I mentioned at the top, lime sulphur has a lot more to offer.

Lime sulphur can be used to control a range of fungal diseases including Black Spot, Powdery Mildew, Peach Leaf Curl, Rust, Shot Hole and most root zone fungal rots. Lime sulphur can also be used to control most insect infestations including Vine weevils, Scale insects, Mites, Saw fly larvae and Caterpillars, Spider mites and Spiders, Aphids, Thrips, Leatherjackets and most anything else that walks or crawls.

Lime sulphur is generally considered safe for bees so long as direct contact is avoided. Avoid contact with bees by spraying during the dormant season or when it’s too cold (typically below 12 Celsius) for bees to be flying. When application is required during the growing season take precautions to avoid bee contact for 24 hours by putting sprayed plants into a closed greenhouse overnight or covering with horticultural fleece. Once the spray has completely dried on the plant it will be safe for bees. Avoid spraying when plants are in flower, it’ll achieve very little and will also discolour and spoil blooms. Never spray Lime Sulphur when it’s hot.

In bonsai Lime sulphur is primarily used as a treatment for the preservation of deadwood. This is achieved thanks to the deposition of sulphur deposits which prevent fungal growth that causes rot. The whitening effect is a secondary benefit resulting from the residual lime within the solution. Lime has good disinfectant properties and will destroy many bacteria and fungi.

How To Use Lime Sulphur –

Preserving Bonsai Deadwood

A simple task but as always there are some tricks of the trade that will significantly improve results. For this task Lime sulphur is used neat, decant from the bottle and don’t put dirty solution back into the bottle or it will contaminate the remainder.

Lime Sulphur is best applied to dried/seasoned and oxidised wood. Recently carved green wood is best left for a year to dry out completely before the first application. Applying to freshly cut wood gives the solution almost no chance to penetrate the surface because of moisture or sap still present. In time the residual lime will begin to flake.

Preserve bonsai deadwood at least once a year, or ideally twice, once in autumn before the winter wet arrives and again in mid-summer when the wood should typically be at its driest (internally) thus ensuring good penetration into the surface.

Applying lime sulphur is simple. All you have to do is very lightly damp the woods surface with a mist spray of water and then apply sparingly with a brush. Don’t apply to wood whose surface is completely dry as it will endeavour to just bounce off. Once finished you will need to allow the product to dry naturally in a protected spot for 24 hours. This ensures the sulphur fully penetrates the wood before rain has a chance to carry it away. Once weathered the wood will become whiter and look very natural.

To learn more about preserving bonsai deadwood see Graham’s article – Preserving Bonsai Deadwood

Winter Washing With Lime Sulphur

Winter washing will significantly help in the control of many fungal and pest problems later in the growing season. Issues like peach leaf curl (seen on many fruiting varieties like blackthorn), elm leaf and other forms of gall and powdery and sooty mildew as often seen on oaks cannot be treated once symptoms are visible. Often visible effects are consequential symptoms of an already active disease or pest. Using Lime Sulphur during the cold weather before pathogens become active is extremely effective.

Don’t use Lime Sulphur for this type of winter washing!

Winter washing is generally associated with deciduous trees, particularly fruiting varieties but the technique is extremely effective at controlling problems suffered by evergreen varieties too. Over the years I have had personal experience of stubborn pest issues like sooty mildews, scale insects and other pernicious pests that, ultimately were all eradicated permanently by winter washing with Lime Sulphur.

Winter washing is a simple and safe process that requires spraying plants with diluted Lime Sulphur. However some precautions have to be taken to make the process safe and effective. First up, personal safety as mentioned above. An old overcoat, hat and hanky around the face might have been ok for your grandad but let’s up our game a little folk. I have been in serious trouble at home for stinking the house out and spent nights on the sofa.

In the UK winter washing is typically done around late February time. Washing too early may reduce the effectiveness. We want to wash as close to spring as we can but too late can cause problems for embryonic leaves as bud scales crack open. If that happens it’s too late and the opportunity has passed. Timing will vary according to local conditions and being a little too early is better than missing the chance by waiting too long.

Use a horticultural pressure spraying device to apply Lime Sulphur winter wash. A trigger spray will not produce an even and effective cover. It only takes a small spot of untreated bark to allow pests to survive. Use a fine misting spray and cover every part of the plant by spraying from above, beneath and both sides, including any deadwood or jin. Spray until the bark is evenly wet but avoid too much run off. Winter washing solution is stronger than that used for soil treatment so try to avoid too much solution running into the rootball though a little will not cause any problem.

Lime sulphur can temporarily discolour or stain some types of pot used in bonsai. Unglazed pots are particularly at risk but many older valuable and antique pots can be marked or permanently stained. Personally I use an old large bath towel that’s slightly damp. This is curled around the base of the trunk so it covers soil and pot in one go prior to spraying.

Evergreen plants are treated in much the same way though I personally tend to avoid soaking the entire foliage. I have found spraying the trunk then spraying branches from beneath is sufficient. Hydrogen sulphide gas is effective at a little distance and the evergreen canopy of foliage will help to retain this for a very short period that seems to be sufficient to get the job done.

After winter washing is complete allow the plant to dry naturally. If rain is expected plants should be placed under cover, like an open greenhouse and allowed to dry. Once the plant is fully dry it will have a ghostly grey appearance, when you see this the plant is safe to place back outside this is typically about 24 hours. After a couple weeks of exposure to the elements the grey colour will magically vanish along with the pests.

Dilution rates for winter washing with Lime Sulphur –

• Deciduous trees without leaves  –  Mix 30 ml of neat undiluted lime sulphur per litre of clean water. (1:33 solution)
• Evergreen coniferous trees  –   Mix 20 ml of neat undiluted lime sulphur per litre of clean water. (1:50 solution)
• Stronger solutions are possible but over the years I have found the above rates of dilution get the job done in almost every circumstance.

Vine Weevil Control Using Lime Sulphur

Vine weevils are literally everywhere these days. Personally I don’t loose any sleep over the little critters but I know a lot of folk do. I am constantly asked for a solution which up until now has entirely centred around the use of Provado whose availability seems patchy, there are a couple of other similar chemicals available. These are typically systemic action products that are extremely effective. However at £12-15 a pop this is going to cost a great deal to treat a half decent bonsai collection.

Mature vine weevil beetle are hard to control because they move around a lot.

Immature larvae develop within the confines of the soil so are easy to get at with Lime Sulphur treatments.

Many folk swear by vine weevil control using nematodes but seeing as I have no personal experience I’ll not run up that particular tree.

If you need a quick, cheap and 100% effective solution for controlling vine weevils and other soil borne pests from leather jackets to wire worms look no further than our little red bottle of Lime Sulphur. I must admit this freaked me out when I first heard it yonks ago but it works and it’s safe!

Vine weevils are small beetles that pose a threat to a wide range of ornamental plants, fruit trees, and vegetables. They are especially problematic during their larval stage, as the grubs feed on the roots of plants, causing significant damage and even death in severe cases (unlikely where trees are concerned). Adult vine weevils, characterised by their dark brown or black colour and distinctive “elephant snout” appearance, feed on leaves, leaving unsightly notches. Fortunately the beetles don’t fly, they walk, and they walk all over the place so controlling them is largely out of the question but the grubs stay put and are easy to get at.

So for vine weevil control using Lime Sulphur we are going to prepare a root drench for application when plants are fully dormant. First up we need to mix a solution of 25ml neat Lime Sulphur per litre of clean tap water (1:40 solution). Pour the diluted Lime Sulphur solution slowly and evenly over the infested soil (which needs to be a little on the wet side of damp prior to treatment) making sure to thoroughly wet the entire root zone. The solution works by releasing hydrogen sulphide gas which sterilises the soil, killing any vine weevil eggs, larvae, or adults present. It also helps in preventing fungal and bacterial diseases that can further weaken the plants.

Treatment in autumn should eradicate grubs and eggs laid over the previous summer. If your plants continue to suffer from Vine Weevil after two treatments, fortnights apart, you can increase the dose rate to 30 or 40 ml of Lime Sulphur per litre of tap water, however, the compost must be wet already, and sensitive or active plant roots may also be harmed by higher doses than this. There are a very few plants that are sensitive to sulphur, these should not be treated, do a little research ahead of time.

Root Drench Treatment Using Lime Sulphur

A root drench is often used to treat either pest or fungal problems hidden within the soil. Personally I have used this technique to control persistent pests like root aphid which can be a pernicious critter that severely weakens the plant it infests. This is also a useful technique to help get on top of hard to eradicate fungal problems like black spot, sooty and powdery mildews and the like. Many of these survive the winter via spores in the soil.

Use a simple solution of 15/20ml per litre of clean tap water and flood or dunk pots, again the soil needs to be a little damp to slightly wet prior to drench. Do this either in autumn once the weather turns cold or in late winter before dormancy breaks.

The best part of using Lime Sulphur for root protection? After a few hours, diluted Lime Sulphur will be fully reacted and is no longer hazardous. It actually converts into plant-available nutrients (calcium and sulphur). As Lime Sulphur has a non-residual action, and is composed of simple chemicals, it can be used in organic growing. Bonsai often suffer from a lack of sulphur which shows as yellowing of young foliage, often mistaken for a nitrogen deficiency.  Lime Sulphur will also combat over acidification of the root mass, a common problem in soft water areas or where large amounts of organic fertiliser are used over extended periods.

If using lime sulphur as a root drench bothers you, and it did me for some time I would recommend using a very weak solution at around 10ml per litre, this can be extremely efficient at preventing problems arising in the first place. This rate is also good for sterilising soil and killing pathogens if you are using any form of recycled soil or material coming from a compost heap or some such.

Scale Insect Treatment Using Lime Sulphur

By far the most difficult and problematic pest issue to afflict bonsai trees has to be scale insect (scale and mealy bug are in the same family). Often this nasty pest goes unnoticed. I remember a lad who came to a workshop a few years ago with a little tree and was telling me how it had amazing bark quality. He was crestfallen when I shew him that crusty appearance was in fact a complete and utter covering of scale unlike anything I have ever seen.

Scale insects that infect bonsai trees can be hard to eradicate but, Lime Sulphur works a treat.

Scale insects belong to the family Coccoidea and are known for their protective, scale-like coverings that shield them from predators and harsh environmental conditions. These tiny pests come in various shapes, sizes, and colours, but they all have one thing in common: they feed on plant sap. Scale insects attach themselves to the stems, foliage, and branches of plants, depriving them of vital nutrients and weakening their overall health.

These pernicious creatures do a lot of damage to most varieties used in bonsai from pines to maples. There seem to be some very specialised types of scale that are hard to recognise, like juniper scale that appears as tiny white spots among the foliage. I’m not here to discuss the unpleasant world of scale but other than physical removal with a brush and methylated spirit (effective to a degree) no commercial preparation I have found will even touch them but…….

If you need to control scale when they are inside their hard shells then a good option is to apply diluted Lime Sulphur. This will act as a fumigant. Lime Sulphur works all year round, so can be applied when the plant is dormant and so there is no risk of scorch damage to the leaves.

Lime Sulphur solution is extremely effective and fast working. It can entirely eradicate scale insect in 24 hours. As an example a while back I obtained an extremely old and mature specimen of Elaeagnus, a beautiful old Japanese tree. When it arrived I immediately noticed it was absolutely covered in tiny white scale insects, by my estimation they had been there for at least three growing seasons. I tried all summer to clean it up with limited success. Once February came around and in a little desperation I broke out the Lime Sulphur and the next day I washed the whole lot away with the hose. Two years later the tree is thriving and not a single scale has returned.

Elaeagnus is a favourite of scale insects.

From being absolutely covered in scale insect to entirely clean thanks to Lime Sulphur application over winter.

For the treating of scale insect across the dormant season dilute 30 to 40ml of neat Lime Sulphur per litre of clean tap water and spray using a heavy mist directly onto the insects which will almost always be on the underside of the branches. Spray the entire surface of the tree and allow to dry naturally for 24 hours.

When treating scale on evergreen trees I personally spray at the end of winter using 20ml of Lime sulphur to 1 litre of clean tap water. This it then sprayed, again with a heavy mist to cover the entire tree including the foliage. Repeat after 2 weeks if necessary.

General Pest Control Using Lime Sulphur

Lime sulphur is primarily used when plants are dormant as we have seen above but CAN be used as a growing season spray. If at any point you are unsure about the use of lime sulphur make a test by applying, as you intend to, on either a small less important similar plant, part of a larger plant or a few leaves growing on a plant in the garden. After a couple of days what you see is what you are likely to get. Always start using a weaker solution and increase the dilution rate for a subsequent application if required. Don’t be afraid to test but always try to use the weakest solution possible in order to get the required result.

Growing season applications can be made when leaves are present but should be applied in the evening when temperatures are cooler to avoid leaf burn. If it’s very warm don’t use lime sulphur. Avoid spraying soft young foliage of broadleaf trees. In general it’s safe to apply lime sulphur solution to conifer foliage so long as the solution is a weaker one and the foliage has been dampened with clean water. Don’t spray immature young foliage that has not fully matured and hardened off.

Before application give the plant a good covering spray with plain clean water. Then mix 10ml per litre of Lime Sulphur to 1 litre of clean water and apply using a fine misting sprayer to infected parts of your plants. Allow to dry naturally outside overnight, keep covered but well ventilated if rain is expected. Once dry return the plant to it’s normal place.

To avoid plant damage caused by lime-sulphur, DO NOT spray when:-
• temperatures exceed 20°C
• when soil is dry and plants are suffering from moisture stress.
• when freezing weather is expected.
• within 14 days of an oil/pesticide or fertiliser spray.

Disinfectant Use of Lime Sulphur

Lime sulphur is an extremely effective disinfectant for general nursery use. It can be used for everything from sterilising compost or previously used pots to sanitising benches and standing areas. Use a solution of 50ml per litre of clean tap water and spray to thoroughly soak surfaces. Soil sterilisation is best achieved by thoroughly soaking using a watering can, pots etc” can be dunked in a container of solution. Sterilised soil should be allowed to sit for a good few days before use.

Lime Sulphur As Bonsai Fertiliser

This is perhaps the most surprising use for Lime Sulphur in bonsai cultivation. The notion that because something smells bad it must be harmful is a modern one borne of our ultra-processed existence. Forget all that, smelly lime sulphur is extremely beneficial to plants as we have seen but FERTILISER! Really?

Bonsai that grow in tiny amounts of soil need to have nutrients added skilfully throughout the growing season. Many traditional and proprietary fertiliser products have little or no sulphur included or present. Up until the 1970s sulphur deficiencies were fairly rare. In the developed world, sulphur was common as dissolved sulphur dioxide; a pollutant from industrial processes. As industry cleaned up its act, and we have moved away from coal-fired power stations, the supply of sulphur nutrition from pollution has dramatically reduced and now needs to be added artificially.

In bonsai our use of largely inert aggregate products as growing media exasperate the sulphur issue. Organic matter can be a good source of sulphur for plants but this is short lived in our limited soil volumes. The widespread use of organic fertilisers like Green Dream,  Biogold or Rapeseed Pellets go a long way towards taking up the slack and supplying important nutrients but over time the cumulative effects can lead to over acidification of the soil. Most plants typically struggle to absorb nutrients from acidic soil and the lower the pH the harder it is.

Most nutrient deficiencies show as yellowing foliage making diagnosis difficult. A sulphur deficiency is a little unusual as it presents as noticeable yellowing of immature foliage. Yellowing is most commonly diagnosed as either nitrogen or iron deficiency but can just as easily be the result of sulphur being in short supply. Additionally if the plants soil has become overly acidic this quickly manifests in much the same way.

The solution is simple. Lime sulphur will quickly reduce the acidity of soil thanks to its lime content thus improving nutrient take up. It will also supply sulphur in a plant available form that’s quickly absorbed. Just add a teaspoon (5ml) or two to a watering can of clean water and apply to soil at any time throughout the growing season. The first application should be in spring as growth gets under way, another around mid summer and the final just before leaf fall and before frosts in autumn. This has the added benefit of keeping pests under control.

Obviously don’t apply lime sulphur to ericaceous plants like satsuki azaleas etc’. There is also no need to apply additional lime sulphur if you have recently used the product as a root drench. Remember you should NOT mix with other fertilisers, apply lime sulphur alone and only mixed into clean water.

In Conclusion – Lime Sulphur – A Miracle Solution

As we have seen Lime Sulphur is a simple, widely effective and safe solution to many of the problems encountered across the infinitely variable world of horticultural P&D control. It has no residual harmful presence in the environment and both elements, the lime and the sulphur are ultimately absorbed by plants as helpful, in bonsai often lacking, nutrients. The only real downside is the short lived smell. In my experience this is no worse than that experienced following the application of a good organic fertiliser and is of little consequence so long as it stays outside.

As with all chemicals Lime Sulphur should be respected, used responsibly and with appropriate safety measures. Diluted correctly and applied with care and forethought it’s an extremely good and effective answer to some very persistent pest issues. Clean up is easy with nothing more than warm soapy water required. Lime Sulphur is a simple, easy and extremely economical alternative to modern chemicals and has been proven over close on two hundred years.

Remember, if in doubt about Lime Sulphurs use begin with a weak solution. You can always test a few leaves or a less important plant just to satisfy oneself your plan is safe. Where application to foliage is required make sure the foliage is damp before spraying. Protect ceramic pots from contact with anything other that weak solutions and don’t use when the weather is too warm.

Finally use a good product from a reputable quality source. Store in a dark cool place protected from freezing and away from animals, kids and NOWHERE near any acids. Do not spray when bees are active and protect waterways from contamination in any form. Don’t drink it or rub it on your boils, absolutely keep it out of any small cuts and ones eyes and other orifices and all should be well.

Disclaimer.
All of the above advice is given freely in good faith based on my own experience using lime sulphur in my own UK garden based on over 35 years of bonsai cultivation. Techniques, dilution rates and timings may vary where you are and dependent upon the product you are using. Always follow manufacturers advice and familiarise yourself with local rules and regulations regarding the use of Lime Sulphur. We accept no responsibility for the actions or outcomes of anyone acting beyond our control.

How To Stop Killing Bonsai Trees – Thoughts On Winter Care

Sep 27, 2023 | Bonsai Tree Care

This gets a bit long, if you are in a hurry you can skip the preamble….

Preamble – BS for starters

Before I get into todays main course please allow me to apologise for the lack of blog posts so far this year. I don’t have a precise explanation for my absence. In modern parlance I feel I have been suffering from what’s known as an acute mental health crisis. That might sound serious because that’s how modern society likes to use language. Back in the days of plain English we would say I’ve been a bit naffed off, fed up or depressed.

Yesterday I fell off a ladder and am a bit banged up so here I am making the most of my straitened mobility.

Now I know a great deal of you lovely people look forward to my ranting, raving and spouting bollocks and I am truly sorry to have deprived ya’ll of a smile but honestly I have been moments away from throwing in the towel this year. I have been ready to close our doors and get a job delivering groceries.

In the words of the immortal Larry Love – Alabama 3 – Terra Firma Cowboy Blues
The world don’t seem to fit me
I’m always starin’ at the stars
A better life for me in some other galaxy
I wanna get off this world of oursI got a telescope on the roof
I’m always searchin’ the stratosphere
’cause breathin’, breathin’ it ain’t easy
In this loveless atmosphere

WTF happened to my country? Great Britain was once the envy of the world or some parts at least. We invented most things and perfected the things we didn’t invent. We largely, by some measure, invented modern civilisation and stood up for its values (with a few inevitable blind spots). We even gave the world our language and now we seem to have literally flushed the lot. We’re in such a f**ing mess our idiot leaders can’t even decide how many genders the human species contains.

Sadly I’m not the sort of bloke to just laugh this all off and when government regulation and rules have cut my livelihood in half I take the situation as seriously as a heart attack. Britons are literally drowning in liquified bullshit and most folk appear to be asking for seconds. Just don’t ask for a straw or plastic spoon, they’ve been banned. If you go to a regular job and spend your time looking at sport I guess life is pretty good. Thumbs up if that’s you, salute!

Personally I have no time for sport. I have never watched a football match in my entire life and the only ‘sport’ i got into for a short while was F1 (IMHO now a load of tosh) but trying to get sports removed from my Sky package this year was almost impossible. I told the guy on the phone I want it removed entirely and after fifteen minutes of refusing my request he’s like “Why wouldn’t you want to watch sports?” In the end I had to say “look you cloth eared c***, you either remove sports or I will cancel my package entirely, then I’ll come over there and shove this box up you hole personally.” Obviously that went down well with a retort along the lines of ‘no need to take that tone’. After an hour and a half I got what I wanted but now they call me up every few days and ask if I would like to get it back. Take my advice, give Sky a wide berth if you can.

Here’s how I lost another 2 hours of my life last week. These days I drive old school Toyotas, the type with a heavy steel chassis and over-engineered diesel engines that do a million miles between oil changes, they don’t break down, but for my good lady’s peace of mind we have, for over fifteen years, paid the AA for breakdown and recovery services. In all those years I have called them out twice, once when my old beater of a Mercedes van wouldn’t start out in the middle of the woods and another time when Catherine’s Mini (BMW) went to shit. I now no longer have German vehicles.

It’s a little known fact that Stonehenge was actually built using a Toyota Hi-Lux. Forget all that Tony Robinson crap about wooden rollers, boats and dragging stones across from Wales, that’s a crock, the Japanese were well ahead of the game as always. The only reason the boffins don’t know this is that they never found it, it’s still running about the middle east with a 50 cal’ bolted in the back. Had the builders used a Mercedes the rotting husk would have been found in the bottom of a deep pit round the back along with the detritus of packed lunches, broken Thermos flasks, busted shovels and well thumbed tatty copies of Mayfair and the Daily Sport.

One of the most influential factors in human development. The Toyota Hilux!

So, I get my renewal through and it’s about £275 because I am their longest standing customer and they really value my loyalty. Now I remember when this cost a fraction of that sum and when I inquisitively look online new members are getting the same cover as me but for just £108. You know what comes next right? I get on the blower and after what seems like a very long time a chipper young fellow answers my call.

I raise my issues but he tells me i’m wrong and my renewal figure is what it costs to actually run the service…..that I don’t ever need to use. So after some back and forth he’s not so chipper any more, I can have that effect on people. I get him to back down and he offers me £50 off which I politely decline. Now I’ve got him on the run I muster the big guns, this is fun and my renewal price ends up at the £108 I can get online as a newbie. He’s so chuffed he got me over the line but my opinion is that if he can offer the service for that figure that’s what it should be all along right? I really don’t appreciate their pissing up my back and telling me it’s raining. I kept them on the phone for 2 hours and never renewed.

The AA are a conning bunch of robbing bastards even if their breakdown service is pretty good in my limited experience. And, just to put a cherry on the cake today I got a letter offering me the service for £39. When I looked into that it actually cost £59 but you get a voucher worth £20 for a posh shop I never use because i’m working class. I remember when the AA was a respected organisation and a British institution to be proud of. I recon they’re a bunch of chiseling grifters these days. If you happen to work for this once august institution i’m sorry.

My glass has never been half full, but this sort of experience is now the norm in our country. Everything is geared towards big business and us little guys just don’t stand a chance. I’m not even going to get into our so called ‘government’ who are hell bent on controlling everything and taking care of nothing. They shit on my head whilst telling me it’s a fashionable new hat the’ve provided for me entirely free which is cool right? But what CAN the little guy who didn’t go to the right school or descend from the right bloodlines do? Well I can spout on about bonsai trees for a bit….

How To Stop Killing Bonsai Trees – Thoughts On Winter Care

So, it would appear I have gotten off track somewhat. My original intention was to put together my thoughts on how folk have been losing lots of bonsai trees this year so here goes……..

I have seen and heard a considerable number of what we might politely call ‘bullshit theories’ alongside some insightful but occasionally ill-thought out conflations about what’s been going on. It’s not just us bonsai folk, right across horticultural disciplines heavy losses have been seen. My only concern is that we learn what we can and not in a “Join the AA for just £39 or £275 for the exact same service” type of way.
So for what it’s worth here’s my two penn’orth……

Anyone remember to winter of 2010/11? It’s actually got a dedicated Wikipedia page. That was a cold one here on the normally mild east coast as relentless onshore winds cut us all down to size but across the whole country it was flippin’ taters. Bonsai tree losses that year were off the scale catastrophic. Previously we had more than ten years of largely mild winters and most of us were lulled into a sense of false security and marginally hardy trees like tridents, Chinese elm, Japanese black pines and Mediterraneans were left outside where, as it happened, they froze to death. I know folk that lost tens of thousands of pounds worth of the most amazing bonsai trees.

During the autumn of 2010 a bargain fell into my lap in the form of a massive ancient cork bark Chinese elm. I picked it up locally for a song and it filled the back of my van. This was a spectacular tree and the best of it’s kind I personally have ever seen. With my then limited experience of the variety I just left it outside for the duration. The tree never came back into leaf and ended up in my log pile and it broke my heart. However I know for a fact it had spent many years outside further inland where it’s always colder in winter than it is here on the coast so what gives?

Come summer of 2011 it was literally impossible to sell trees of any type, the whole community seemed to be reeling from heavy losses and were too shaken to start filling up their benches once again. Confidence was severely undermined and it took all of us a long time to get over what we had experienced. However we largely have short memories and by the following year everything was back to normal though lots of folk set up overwintering facilities which were largely not needed as winter temperatures returned to normal.

This last year was an odd one and that makes it hard to read or understand why problems have been so widespread. Certainly where we live the temperatures didn’t get that low. We got -5° C where we would normally see -1°C at worst but then that’s hardly a low temperature where hardy plants are concerned. We had some wet patches too but nothing particularly unusual. Last summer was nice, warm and sunny. Forget the media hype it was a beautiful warm and sunny summer but, for heat, not a patch on what our friends in Spain or Italy experience every year and they do just fine. Most folk across the country lost something so it’s not down to the individual so what? What went wrong?
 

The activity of plants are dictated by light. Wiki’ states…..
“Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods. They are classified under three groups according to the photoperiods: short-day plants, long-day plants, and day-neutral plants.”

What this means is that our little trees sense the daylight hours increasing in spring and begin to move into a growth phase. The rate or speed of that growth is dictated by temperature but it’s not triggered by temperature. That’s why a hawthorn may be showing red buds by mid-January when folk begin to panic and demand I send their soil by emergency courier because they MUST re-pot today. However the temperatures in January are normally what’s locally known as ‘basterd cold’ and so whilst your beloved thorn may well be showing signs of life it’s literally months away from developing proper leaves until day length and temperature increase a good bit.

Now this photoperiod is not just responsible for triggering spring growth but everything a plant does. Leaf formation, shoot extension, flowering, fruit set, secondary hardening of growth, root formation, wood production, the next seasons buds and WINTER HARDINESS are all dictated by day length. When the days are long most plants are growing for all they are worth because certainly in Blighty the summer is pathetically short and light intensity is never ideally high. As the light fades later in the year, shoots are done growing, roots are formed and the following seasons buds are in place a tree will begin to mature new growth and prepare for winter. The general consensus is that they need night time temperatures down to +5° C for a few weeks for this to kick in. What happens inside the tree varies by species and it’s too complicated for us to fuss over.

Last years nice warm summer was an absolute belter and our trees, assuming we took advantage, should have had an amazing year which based on my own experience they certainly did. Plants ONLY get their energy from the sun and a nice bright one means our trees have high energy levels and should be able to get a lot done and be tough and resistant to just about anything. However last year temperatures were high late into the autumn and then cold came in early. On the coast here temperatures never drop below freezing before mid-January onwards. Last year that happened in early November whilst a great deal of my deciduous trees were still in full leaf.

As the day length begins to shorten significantly a plant has a lot to do in a short period though to us it might not appear to be all that. Just because a tree is not growing or has no leaves don’t think for a moment nothing is going on because it IS. So, what’s happening?

A tree in full leaf stores a great deal of its energy, in the form of sugars, in the foliage. The development of fall colour happens because a tree is preparing for winter and will draw out as much valuable resource from every leaf as it can starting with the green chlorophyl. Once the process is complete most deciduous trees instigate a process known as ABSCISSION from Latin ab- ‘away‘, and scindere ‘to cut’. This causes the leaf, or fruit, to drop.
A plant will abscise a part that is no longer necessary, such as a leaf during autumn, or a flower following fertilisation. Most deciduous plants drop their leaves by abscission before winter, whereas evergreen plants continuously abscise their leaves. Another form of abscission is fruit drop, a plant abscises fruit while still immature in order to conserve resources needed to bring the remaining fruit to maturity.

Abscission occurs in a series of three events:

1) Resorption –
Resorption involves degrading chlorophyll to extract the majority of its nutrients. Nitrogen is found in chlorophyll and is often a limiting nutrient for plants, which need large quantities to form amino acids, nucleic acids, proteins, and certain plant hormones. Once nitrogen and other nutrients have been extracted from chlorophyll, the nutrients will travel to other tissues of the plant. Resorption is what causes leaves in the fall to change colour. Carotenoids in the leaves are slower to degrade than chlorophyll, so autumn leaves appear yellow and orange.

2) Protective layer formation –
Cells under the abscission zone divide and form a layer of cork like cells. Situated on both sides of the abscission zone are layers of parenchyma cells, which produce and inject suberin and lignin under the abscission zone into the new layer of cork cells. Suberin and lignin create a durable and waterproof layer for the plant once the element is detached.

3) Detachment –
This step can occur in a variety of ways depending on the species but always occurs at the abscission zone. Detachment can occur when layers of parenchyma cells secrete cell wall enzymes to self-digest the middle lamella or membrane, which holds the cell walls together at the abscission zone. This causes the cells of the abscission zone to break apart and the leaf or other plant part to fall off. Another way detachment occurs is through imbibition of water. The plant cells at the abscission zone will take in a large amount of water, swell, and eventually burst, making the organ fall off. Once detached, the protective layer of cork will be exposed and the area is protected and sealed off from the outside world.

Another thing a tree must get done before winter is the hardening off of new growth and roots. This is achieved by the formation of lignin. Lignin (woody tissue) is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity and do not rot easily. Chemically, lignins are polymers made by cross-linking phenolic precursors. Simply put, soft vegetative tissue become fibrous which gives it the ability to resist the effects of freezing. This happens throughout the summer and autumn. Last year I had maples making strong extension growth throughout September and the first half of October. Most of this did not harden off fully before the frost came and as a result was lost to the cold.

By now it’s obvious there’s a lot more going on here than might appear to be the case from casual observation. A bonsai tree is a tree largely cultivated in a very un-natural situation and very often a very long way from it’s natural environment. For instance mugo pine growing in the Alps stand temperatures below -40C in winter and are often buried in meters of compacted snow. The roots are frozen solid for months on end and therefore bone dry. At sea level where, certainly in this country it’s not frozen for most of the time but it is sopping wet thanks to rain and cool conditions the roots are waterlogged for months on end and so can rot. So a tree that lives in one of the most extreme climates in Europe can die spectacularly in a soggy warm British winter which brings me neatly onto my next point.
What’s the deal with freezing? Without water there would be no plants….or any other life come to that and, much like the other ‘water of life’, in the right place it’s a great asset. However too much can be a bad thing and too much for too long is almost always a very bad thing. One can go from being lucid to ludicrous to hospitalised in a very short time much like a bonsai tree though the latter’s going to show delayed onset of symptoms.

It’s commonly stated that 50% of a tree’s weight is water. But the moisture content of different living tree species can range from 60% to 200%, where there’s twice as much weight from water as there are wood fibres. So obviously this is important.

It’s a very long time since I went to school and back when I did go I didn’t actually go very often. Even when did go to class I was far from a model student and spent my time being a right little knob. One subject I did okay in was physics, it seemed like a lot of common sense to me apart from all the equations of course. One thing they did teach me was about water, it provides a reference point for things like temperature scales etc’. That’s because it’s everywhere and very easy for folk to reference. It can be solid, liquid and gas all within a fairly narrow range ie: from freezing to boiling point.

When water freezes it expands. As a liquid the molecules huddle closely together but as the temperature falls and the water cools down, the intermolecular forces increase, the freedom of movement of water molecules decreases, and they become less and less energetic the colder they get. When water reaches its freezing point, the movement of its molecules become negligible as they take on a more defined shape, arranged in six-sided lattices. This crystalline arrangement of water molecules is less dense, as it prevents molecules from huddling up due to stronger intermolecular forces. This spacing of molecules and keeping them fixed in that position increases the volume of water, which is why it’s said that water expands when it freezes. Typically freezing water increases it’s volume by 9 > 10%.

Trees are a naturally closed hydraulic system made up of cells, think of those cells like inflated tea bags. Put a row of them together and fill one with water and before long the water will be dissipating into the adjacent ‘cells’. There is strong cohesion between water molecules because of hydrogen bonding. A continuous column of water is therefore pulled up the plants stem in the transpiration stream by evaporation from the leaves. As water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots. When water freezes it expands putting pressure on the cell walls. If these are not sufficiently strong, as in the case of tender plants, to accommodate the expansion the cell walls rupture and the water column will be broken. Where this happens extensively the plant may not be able to repair itself or recover. The damaged area and that above it will eventually die completely.

Here’s a couple of amusing examples from my own refrigerator, a place in our house where good vegetables go to die. I recently found a bag of rather disturbingly shrivelled soggy looking carrots. Some were not rotted but could easily be bent end to end. I gave them a rinse and put ‘em in a glass of water. Two days later they were as good as new, rock hard and as firm as the day they were plucked from the ground. I ate the lot and they were good. Just like the tea bags the water soaked from cell to cell until everything was back to normal. No, i didn’t put Viagra in the water!

I currently have a lot of cucumbers in that same fridge. Some have been there for weeks and are floppy but some are nice and fresh. If I were to put one of each in the freezer overnight upon defrosting the rigid one would largely turn to liquid because it’s thin cell walls are broken and the water will escape, it’ll be a mess. However, the soggy one will be in a slightly better state and this is the salient point because, at the outset there was less pressure on the cell walls which allowed for the expansion, less damage was done and less water is lost and we can make some nasty soggy sandwiches with it.

Frozen water (ice) is dry….obviously. It’s why your freezer keeps food good for years on end because where there is no water bacteria cannot ply its trade. Our Alpine mugo pine survives months without water over the harsh frozen winter but how? In very severe cold climates native trees remove water from their cells, tolerating the dehydration of the cell contents, and place the water between the cells where it can freeze without causing damage. This works where the weather provides a prolonged slow descent into extreme cold.

Larch roots desiccate in winter and should we be poking around down there too early it the season they appear dead, just a black outer membrane and a thread down the middle. However all is well because come favourable conditions the root will reinflate itself and carry on as before. It’s a protection measure to prevent roots from freezing damage. Bear in mind larch grow very well with wet feet in damp places where simply shedding water is not possible. Most plant species and tree species in particular have what often seem fantastical winter (or summer) survival strategies to deal with extremes of climate.

From the above it’s obvious we may need to consider the effects of water in relation to overwintering our bonsai trees. In some instances we may need to take some practical measures but as always consider your actions carefully and go steady.

Temperature is another factor that can have a significant effect on trees in almost every aspect of their existence as we saw earlier. Thankfully here in GB we don’t see those extremes. I say that because I believe the British media are a bunch of tossers (by and large) we do not have extremes. We have what’s called a temperate climate ie: those without extremes of temperature and precipitation. The changes between summer and winter here are invigorating without being frustratingly extreme. There are two types of temperate climate: maritime and continental. The maritime climate is strongly influenced by the oceans, which maintain fairly steady temperatures across the seasons. Since the prevailing winds are westerly in the temperate zones, the western edge of continents in these areas experience the maritime climate. Such regions include western Europe, in particular the UK, and western North America.

I won’t be delving into the intricacies of that particular aspect as it’s not really a concern for us. However do bear in mind not all trees or their multitude of species and sub-species are the same and so knowing what you have and understanding its natural range is important. As an example take the genus Acer this contains the varieties ginnala (Amur maple) and buergerianum (Trident maple). The former can withstand temperatures down to -45C whereas the trident will be dead around -6C. So, know your plants.

We can see, thus far, that getting our precious bonsai trees through an unpredictable British winter is always going to be a bit of a weather based crap shoot. Earlier I remarked that a bonsai tree is a tree largely cultivated in a very un-natural situation and very often a very long way from it’s natural environment. Our mugo for example is a fish out of water here in soggy GB. However plants are tough and adaptable which is why we get away with what we do.

Bonsai are never going to have a large enough root system to really thrive. Anyone who has grow material in the ground will know how fast a tree can bulk up once established. Compared to pot cultivation the development rate can be 10x faster. Mother earth knows how to take care of her trees. I also wrote here years ago about how capillary action turns a shallow pot into a puddle in winter. Also bear in mind a tree with its roots in the ground enjoys a fairly stable temperature. In winter even if the surface is frozen solid, just a little below the surface it’s +4°C. A bonsai trees roots will be almost the same temperature as the ambient air. Plants in the ground don’t typically see more than a few degrees of temperature change whereas a bonsai could easily see a 20 or 30 degree swing in as little as 12 hours, particularly in summer or during a cold snap. That’s unnatural and a tree like trident maple will not cope but then our mugo pine is going to be just as vulnerable because at the altitude where they occur naturally in never gets warm, even in summer. A pot sitting in direct sun in summer can easily hit 40°C or more. Ever seen one steaming when you water in the early evening?

Having set out in brief (???) some of the more significant points concerning the survival of bonsai trees over winter please allow me the indulgence of expressing some personal opinions and observations. Because we are clever bastards we can grow trees in little pots, many are tough enough to stick two fingers up at us and carry on regardless but some are not.

Most of the bonsai trees that end up dead are not the result of weather, disease or pests. Dead bonsai are almost always killed by their owners though likely not on purpose. Nowadays we refer to that as abuse, a widely used and abused term. Abuse is when someone causes harm or distress. It can take many forms, ranging from disrespect to causing someone physical or mental pain but in this case most often it’s a case of neglect and ignorance.

In bonsai we can define the term as not providing the appropriate conditions and materials for our charge to thrive and survive. Like a customer of ours from years ago who spent a lot on a stunning tropical variety of bonsai and insisted in keeping it inside his log burner (the doors were open) all year. It looked nice apparently but as I warned him that wouldn’t last long and it didn’t. It never ceases to amaze me how newbies know so much more about bonsai than those of us who have spent our lives learning. Ya’ can’t educate pork!

In order to get a bonsai tree through the winter in tip-top condition it’s important that it’s in tip top condition long before the winter even starts. In my experience (we buy a lot of bonsai collections) the larger part of trees called bonsai in this country are no more than a harsh winter or two from the compost heap and so when adverse conditions come along, way too many are left with little defence. Kind of how many folk are just one or two pay checks away from financial oblivion.

I write here ENDLESSLY about inappropriate re-potting of bonsai trees and that’s a VERY significant reason why so many trees die over winter, they just never get to build a mature root system or reach a stable equilibrium.

Case in point, back in 2019 I recounted The Tale of Two Maples. It’s interesting to look back and that sorry little deshojo featured, it’s still with me, just compare these pictures taken four years apart at the same time of year. Which do you think will stand the best chance of surviving the winter?

Deshojo maple bonsai September 2019. Not looking good.

Deshojo maple bonsai tree. September 2023. Hale and hearty. This will go through a tough winter safely.

It’s a long story for another time but illustrates my point, we need to work hard, sometimes by not doing things, to ensure our trees are supremely healthy at all times. That way they are going to shrug off adverse conditions much more readily than not. Only a fool would expect a pint swilling, pie eating 40-a-day sofa spud to go run a marathon successfully. That’s got disaster written all over it. But, a poorly bonsai tree in an inappropriate pot, the wrong soil structure, badly situated in the garden that’s been badly pruned to the point of weakness and poisoned with inappropriate use of fertilisers, pesticides and fungicides does not come through a bad or unpredictable winter and everyone goes looking for some exotic disease or similarly lame reason to excuse their own long term failure. Others, and I have heard this a thousand times tend towards the “it just died, I don’t know what happened, it’s been fine for years” type of platitude.

I’m yet to see, or hear, of any tree that committed suicide. Given appropriate conditions trees don’t die wether they are in a pot or their natural environment. Where a tree in nature does die it’s because things have changed, trees have grown up around it, successive dry or wet seasons excess or lack of sunlight or nutrient poverty. There’s always a reason but much like our dead bonsai trees after a rough winter it’s not always obvious even though everything we need to know is right there. Trouble is once the piece of paper with the verdict is handed over 9 times out of 10 it’s got our name on it hence …… How To Stop Killing Bonsai Trees – Thoughts On Winter Care

If you have managed to read this far I’m betting your head’s going ding-dong about now so by way of a little light relief lets look at some practical examples based on my experience. There can’t be many of us that have not or do not have trident maples. Now I already touched upon their being particularly susceptible to freezing. This year I lost count of the folk calling me for advice on the variety so what typically happens?

Tridents, much like Chinese elm are really warm weather trees. They grow at least 6x faster in a greenhouse than they do outside in my garden. In the winter, assuming the soil is very dry they will be okay down to about -5°C but if their soil is really wet or waterlogged, which is almost always the case outside, they won’t. A combination of thick fleshy root structure, the soil we tend to use for thirsty deciduous bonsai, shallow pots and pretty moss coverings to the soil surface all mean a tree sitting outside under the sky is likely to end up very soggy. When this freezes hard the roots, other than thick lignified parts, are quickly lost due to excess internal water expansion and hydraulic pressure from outside. Just try adding an additional 10% of soil into an already full pot, hydraulic pressure caused by expansion of freezing water is easily sufficient to bust open even the largest and strongest ceramic pot. Just think what it’s doing to soft tender roots.

Now assuming this maple was going great guns all summer and shut down correctly in autumn it will have stored a lot of energy in it’s woody structures. Come spring time the tree will leaf out like normal but then growth will slow really quickly, leaves may be normal to begin but as a shoot develops the size rapidly decreases before typically the end of the shoot stops, may droop, discolour and eventually dry out altogether. Other leaves are lacklusture and will quickly discolour, curl up, or down and all activity quickly ceases. At this point most folk start thinking about ‘feed’. That’s a bullshit expression as I have said before, you can’t feed a plant but enough of semantics.

What’s happened in this example is that the tree has stored it’s previous seasons energy like a battery. At the appropriate time this has fired up and got the motor running. Trouble is over winter some little bastard came in and syphoned off the tank so there’s nothing behind the battery to really kick up the activity after the starter got us running so progress quickly stalls. The tree remembered it had a root system so chucked out an appropriate amount or new growth which quickly collapses because the frost took the roots away. Because most or all of the roots are gone the water column collapses, foliage cannot be supported and most times the tree will eventually die completely though, typically it’ll linger until well into the second half of summer, teasing you all the way.

At this juncture some bright spark’s going to ask what’s the difference between a tree that’s had it’s roots nicked by frost versus one that’s had them all chopped off in an overly enthusiastic re-pot. Trust me there’s all the difference in the world but my heads now getting too tired to explain. Health, vigour, timing and new soil all have a part to play

Sometimes a bonsai tree in this condition can be saved but it’s not an exact science. As discussed, a supremely healthy tree has significantly better odds. What has worked for me, and others I have shared this with is as follows. Keep under cover protected from rain exposed to as much sun as is possible and out of the wind. Assuming there are leaves do not mist, spray or foliar feed, we’re on battery power here. Keep the soil dry, if there is moss remove it entirely so you can see the actual soil. A small weed or two is helpful. When the weed wilts flat onto the soil you know the moisture level is about right. The most critical element of this is that soil moisture level and maintaining it right on the edge of almost too dry.

What we are doing here in effect is rooting a big cutting and if luck is on our side and damage is not too extensive it will work. The combination of a little stored energy and some small input from the leaves might just be sufficient to fire off a few small feeder roots which in time will develop sufficiently to restore the water column. Think of Bear Grylls making a fire from a spark. A tiny fleck of dry tinder smoking lightly, with care develops into an ember that’s slowly cultivated into a tiny flame and so on. Once new extension growth, which should be left to aid recovery, is romping away at one or two feet long we can begin the application of a tiny amount of fertiliser. Once you have seen good autumn colour and a text book leaf drop, breath a sigh of relief.

Bearing in mind what I said earlier about the effects of light and temperature on preparedness for winter. Where trees are grown in a greenhouse or polytunnel it’s fair to expect much faster development than is possible outside in most parts of our country. My advice is come mid-August move deciduous trees outside into full sun and an exposed position. This will ensure the tree shuts down for winter in the appropriate way and time frame. Where trees like trident are concerned I would move then back inside after a couple of light air frosts. Good air circulation and soil moisture management will ensure the tree emerges from winter as fit as a butchers dog. Where trees are put inside for the winter but not intended for greenhouse cultivation in summer move them outside by the end of winter. Don’t worry about light air frosts but if temperatures are likely to drop more than -2C you’ll have to hump ‘em back in for a while.

Evergreen trees used for bonsai that are particularly susceptible to British winters include yews (taxus), Mediterranean broadleaves like olive and Holm/Barbary oaks and Japanese black pines. Yew will do best if it’s soil is bone dry over winter. Yews hate wet feet at any time of year and whilst they may tolerate a wet winter it’s just a matter of time before Phytophora (The Plant Destroyer), a genus of water borne moulds finds just the right opportunity to kill your beloved tree stone dead in just a few weeks. Water really is the enemy of overwintering bonsai in Blighty, significantly more-so than the cold. I know folk will kick at that because their yews have been outside for decades. However just look at the losses this year country-wide. I lost yews like that decades ago but since adopting the above action, and late summer re-potting i have not lost a single leaf from a taxus over winter.

Where pines are concerned things are much the same. Most varieties of pine have relatively poor root systems and the tree relies heavily on it’s interaction with mycelium, a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. This collects water and nutrients which it passes onto the tree in exchange for sugars from the leaves. If this fungi is in poor condition pines quickly become weak with poor foliage colour and reduced growth. Mycelium seems to hate wet conditions, particularly when water freezes in its direct contact. One of the reasons coarse soil mixes are recommended for pines is that drainage is good which promotes development of mycelium as well as allowing large volumes of space between particles for the fungus to occupy. Mycelium allows trees to colonise areas that really do not have enough water or nutrient to support them without the interaction.

To keep a pine tree happy just make sure the conditions are ideal for it’s supporting mycelium and all will be well. This, once again means managing soil moisture over the winter but with the added complication of finding enough light. I’m reminded of the time a few years ago that I came by the most incredible 5 trunk kabudachi Japanese white pine. A massive mature 5 trunk bonsai tree and the best of it’s kind I have ever seen in GB. This came as a PX from a customer in the central belt of Scotland. It arrived here and instantly I could see it was not happy, it was yellow. Being September I was aware there was little time to correct this before the cold arrived. The tree was also covered in algae and lichen, it had obviously been too wet for much too long, not an uncommon problem in that part of the world.

To remedy the problem I immediately set it up in the centre of the polytunnel where the through-draft was significant. I then put a large growlight directly over it’s apex set to run 3 hours either side of dawn/dark to extend it’s day length. After the moss was stripped and I got rid of the lichen and algae I crossed my fingers and waited. By early December, with not a drop of water for over 10 weeks the tree was a pristine blue and the mycelium was growing out of the pot. I then dispensed with the light and it went through the winter perfectly and the yellow never returned, I never did re-pot it or change the soil. Old bonsai need careful and intelligent management if they are to live their best lives.

Finally please allow me to make some observations about spring. Back when I started all this malarkey decades ago spring time was end of march to early June. The Met’ office conveniently dissects the year into four quarters based on the typical weather which as we have seen is much less important to plants than is the daylight. The fact some feckless weather presenter tells you it’s spring because of the date does not make it so from the point of view of your precious bonsai. I wrote at great length about this and it’s relation to repotting bonsai previously When To Re-pot Bonsai Trees. It’s spring when a particular tree begins to grow, not just swell buds but open out and grow. This is one of the most valuable lessons I have learned in well over thirty years of fanatical bonsai work.

This last year really did test this notion for me. We like the idea of seasons and a nice defined difference between them all but, living in Blighty that’s just not possible. August 2020 saw us endure single figure temperatures below +5°C and this year whilst most folk were sweltering in a mini June heatwave here on the east coast temperatures were more like early April thanks to biting cold northeasterly onshore winds. I dare say many of you have similar tales of the place you call home.

So based on my own advice my collection of big old Chinese elms were pushing genuine leaf come mid-March and this was really happening fast probably down to a surfeit of energy from the previous, amazing summer. I got a bit caught up in the moment with uncharacteristic enthusiasm and got my re-potting done. However I should have listened to my typically negative inner voice but wishful thinking got the better of me. March is not largely ‘plant spring’ even if it is meteorological spring and I ought to know better at my age. Talk about pissing on your chips!

What happened next was that the temperatures dropped. February is normally not so bad here if the wind does not come from the north or east and this brings things on quickly. That almost never lasts and cold’s never far away. So this year by end of March it was colder than it had been at any point over the winter and it did not warm up to an appreciable degree (by which I mean steady night time temperatures of +12C or above) until the third week of June. So my elms were getting ready to go in March when I foolishly cut their root systems back by 60-80% and then almost immediately we got back down to low single figures by day and frosts at night, new roots didn’t grow and sap froze solid.

What I managed to achieve was a great success in bringing my elms through the winter only to inflict the damage of a harsh winter upon them in my silly enthusiasm and blind hope of a nice summer. Thankfully nothing was lost though none of the trees made growth worth a damn. I lost an entire seasons development which if you know Chinese elm you will know that’s quite a loss. By comparison I bought in a couple of big monster elms in the spring which were not repotted and they have grown about 2-3 feet alongside mine which have made 3” at best.

This whole subject is so full of ifs and buts it’s impossible to give precise advice on what to do for the best. It’s important to keep our whits about us, look at the bigger picture and not just rely on what may have worked for years on end. Overall the best plan is to have extremely healthy bonsai. If your tree does less now than it used too or shows any signs of distress or slowing down, like poor growth, early leaf drop, naff colour or not drawing water from the soil strongly beware. Remember water is more an enemy than cold and never, for a minute, trust the weather. Keep in place a good care regimen of appropriate watering and fertilising (with a season appropriate product) across the growing season. Keep your tree in an appropriate place based on its natural habitat and only water once soil begins to dry out. The constant drying and wetting of bonsai soil is a key element in our success, excess wet is often a very significant part of failure. Most trees roots require moisture but not water and keeping that constant is our challenge.

This subject is broad and deep and I feel I have barely completed an introduction here. Accept my apologies if I have missed anything, i’m doing my best. However after 2 days writing my head is fried and I have other things to do but hopefully this has been a help in casting a light on what happens when we get a bad winter. The takeaway is this….. Trees don’t die, most of the time they are killed by our ham-fisted oafishness and misguided well meaning ‘care‘. Sometimes it takes us a few years to kill our bonsai. Bonsai requires constant vigilance, understanding and effort and a relentless dedication to our own education. It’s not about having the latest ’snake oil’ wonder product or some special soil mixture or ingredient. Success in bonsai is about knowledge and experience and care, it’s about effort, hard work and dedication, often to the exclusion of almost everything else. If you have to stop your bonsai activity to go eat success is going to be a challenge.

Please feel free to comment or contact me by email if this has raised questions and i’ll do my best to respond. If you did manage to read all of this then I salute you. Sadly i’m fresh out of medals but you deserve one 😉 Thank for your time and support, please share!

Graham