Category Archives: Keeping Bonsai Healthy

Foliar Feeding

Some products advise spraying them on the leaves of your trees – a process known as foliar feeding. At first glance this makes no sense, as plants synthesise everything they need from nutrients obtained from the soil and air and these nutrients come up with water through the roots and xylem. And leaves haven’t evolved for nutrient uptake, they have evolved for photosynthesis.

But could this actually work? Well, in order for the nutrients in foliar feed to be useful to plant cells, they would need to both penetrate the leaf and enter the cell.

Can substances on a leaf surface enter the leaf itself? For the most part they can’t as leaves are covered by a protective waxy layer known as the cuticle (described in the post Leaf Structure). One of the main roles of the cuticle is to stop pathogens and other environmental stressors entering the leaf.

But as so often happens with systems of mind-bending complexity like plants – it’s not that simple. For one thing, we know leaves have stomata which allow gas to enter the leaf. But it also turns out that the rest of the cuticle isn’t completely impregnable. The cuticle has tiny pores in it at the base of trichomes (hairy projections) and glands – these range from 0.45 to 1.18nm in diameter^ref. One study did indeed find that dissolved nutrients can enter the cell through these pores in the cuticle: “penetration of ionic compounds can be fairly rapid, and ions with molecular weights of up to 800 g mol(-1) can penetrate cuticles that possess aqueous pores.” The key term here is ‘aqueous’ – the pores need to be wet in order for nutrients to enter through them. For example carnivorous plants use this process to bring nutrients in from their traps via the pores in glands^ref.

A great article summarising the physics of nutrients entering a leaf is here – they conclude that it’s easier for positively charged ions (calcium, magnesium, potassium, ammonium-form nitrogen) to enter via the cuticle pores whilst it’s not as easy for negatively charged ions (phosphorous, sulfur, nitrate-form nitrogen). Similarly smaller molecules or those with a smaller positive charge are easier to translocate around the plant – including ammonium, potassium, and urea. Larger molecules will stay close to their point of entry, including calcium, iron, manganese , zinc and copper. Another study states that younger leaves are less able to transport nutrients out and so applying foliar feed to developing leaves may result in the nutrients staying within the leaf (which perhaps is an effect one might want to achieve?)^ref

So it seems that some amount of foliar feed may be able to enter via the cuticle’s aqueous pores, and a subset of this may be able to move around the plant.

But what about the stomata? Previous studies have said that “the combination of cuticular hydrophobicity, water surface tension and stomatal geometry should prevent water droplets from infiltrating the stomata”.^ref (ie. water can’t get through stomata) but apparently dissolved ions can in some circumstances, because the ions change the surface tension properties of the liquid. This study ‘confirmed the stomatal uptake of aqueous solutions’^ref; but also said this depended on whether the aqueous solution was chaotropic (reducing water tension) or kosmotropic (increasing water tension). So it’s easier for the ions on the left to enter via the stomata, and harder for those on the right.

from: https://water.lsbu.ac.uk/water/kosmotropes_chaotropes.html

But once in the leaf, can nutrients be used by plant cells? It seems so, in some cases, but the evidence is extremely varied and there are many different variables to untangle.

A research study was conducted by ‘Christmas Tree Specialist’ Chad Landgren for the Oregon Department of Agriculture in 2009 comparing foliar feeding to other forms of nutrient application^ref. They tested a range of approaches on blue spruce, Atlas cedar and four varieties of fir (abies), in pots and in the ground, using application methods including “helicopters, mist blowers and various backpack sprayers”. Their conclusions were: “Each conifer species and site are potentially different with regard to nutrient needs and response. Blue spruce appears rather “immune” to foliar application… Nordmann fir appeared to pick-up some of the foliar fertilizer… on other sites, no treatment (soil or foliar) appeared to move the foliar nutrient content levels.”

In another paper^ref the author concludes that “foliar application of particular nutrients can be useful in crop production situations where soil conditions limit nutrient availability.” and that fruit can benefit from direct sprays, but also that “applying fertilizers to leaves (or the soil) without regard to actual mineral needs wastes time and money, can injure plant roots and soil organisms, and contributes to the increasing problem of environmental pollution.”

And then of course it’s not just the leaves themselves. We now know that there is a phyllosphere – a symbiotic community of microbes in and on the leaves which perform a whole range of functions for their hosts, one of which includes producing cytokinins
that can be bioactive within the plant. If foliar feeding increases these bacteria, there may be effects throughout the plant not just on the leaf.^ref

The message from all of these seems to be that foliar feeding may work for leaves or fruit with specific mineral deficiencies which need to be corrected in-situ, if the nutrient in question can get through the cuticle or stomata. Or for plants which have environmental reasons for not being able to access nutrients through their roots (like pH?). But there needs to be a specific requirement in a specific location on the tree for it to make a difference – and it will be dependent on the species, environment, nutrient etc. In most cases I would say it would be better to provide the roots with the requisite nutrients instead.

Phloem

The word ‘phloem’ comes from the word for bark in ancient Greek. It is a parallel system to the xylem which transports water and nutrients up from the roots, but instead transports the products of photosynthesis (‘photosynthates’) from the leaves to the rest of the tree. A big callout to The International Association of Wood Anatomists for the images in this post, contained in this open-access publication.

One of the main photosynthates produced by trees’ leaves is sucrose (maple syrup anyone?), but others found in phloem include fructose and glucose, sugar alcohols and the raffinose family of oligosaccharides (RFOs). A sugar alcohol known as ‘D-pinitol’ has been found in substantial amounts in gymnosperms^ref and is believed to be the main carbon transport molecule for Scots pine. In addition to sugars, the phloem system is used for signalling and defence throughout the tree (as is the xylem), so plant growth regulators (including auxin, cytokinin and salicylic acid), proteins, minerals and RNA travel in the phloem sap as well. If a foliar insecticide/herbicide/fungicide has been applied and is able to penetrate the pores or stomata (see foliar feeding), and is able to get into the phloem vs staying inside adjacent cells, it will translocate throughout the plant.^ref As a result I would not be eating non-organic maple syrup (previously paraformaldehyde was used to reduce microbial attacks on maple trees for syrup product, but this was banned by 1989).^ref

There still seems to be quite a bit that’s unknown about how phloem actually works – an article published in 2014 said “Because of the difficulties in measuring phloem function, particularly in trees, we lack a basic natural history and phenomenology of tree phloem”^ref and another published as recently as 2021 said “phloem loading strategies in gymnosperm trees have been only tested in three species: P. sylvestris , Pinus mugo and Ginkgo biloba.”^ref

But the basic principle is that sugars are created by the process of photosynthesis, ‘loaded’ into the phloem cells (with assistance from adjacent cells) and transported to places in the plant where they are needed, then ‘unloaded’ (but even the mechanism for transportation of sugars in phloem is debated – a famous theory involving ‘osmotically generated pressure gradients’ has dominated but many recent articles point out the lack of data to support it.^ref) According to one account, sugars are loaded from leaves into phloem companion cells by active transport (a process which consumes energy) and then diffuse into the sieve tube elements through the plasmodesmata (cytoplasm which is shared between cells via small pores between them). Water then moves by osmosis into these cells (creating the phloem sap), and sugars translocate (move) when sinks (areas of the plant consuming energy) remove sugar and reduce its concentration in the phloem sap.^ref

Phloem is also believed to translocate (move from one place in the plant to another) sugars even when photosynthesis is not taking place – eg. in winter in deciduous species.^ref In this case the sugars are coming from storage tissues in the rays and roots.

The cells which make up the phloem system in gymnosperms are different to those in angiosperms (similarly to the difference in xylem), but the basic structure for both is that tubular cells, known as sieve cells (gymnosperms) or sieve tube elements (angiosperms), are connected together via pores in their end walls, and the phloem sap ‘flows’ through these sieve cells/tubes.^ref

Below is an image of pine sieve cells. The side and end walls are structurally similar, unlike the sieve tubes of angiosperms. The phloem sap flows from cell to cell downwards, through the pores. Many studies reference the fact that sieve cells & tubes contain material which would appear to create a barrier to flow, which calls into question the abovementioned ‘osmotically generated pressure gradients6’ theory.^ref

https://search.library.wisc.edu/digital/AVCQSJHVTUYFUP9D

If you’ve read the post about the cambium, you’ll know that there is a constant process of creating new xylem and phloem cells, and in the case of phloem, the most recent does the conducting.^refThe conducting phloem usually lasts for one season, but can remain ‘functional’ for one-two years (ie. the cell is still alive, even if it’s not conducting phloem any more). Like xylem, phloem rings are created – see the image to the right of pinus strobus – all of the dark cells are the annual phloem sieve cells which are now non-conducting. The conducting cells are in the lower purple region.

https://scholarlypublications.universiteitleiden.nl/access/item%3A2951200/view

A key difference between xylem and phloem is that phloem cells are living cells. This means that phloem sap must pass through living cells and their membranes in order to flow and this article^ref suggests that this mechanism provides a high degree of control for the plant in managing what gets into and out of the phloem system. The phloem passes through holes in the sieve cells known as sieve plates (see pics below both of ficus species, the left hand side shows a transverse section and the right hand side a lateral section).)

In order to create the space for the phloem sap, sieve cells and tubes are missing quite a bit of the normal cell machinery, including a nucleus, vacuole and ribosomes – so they can’t control their metabolism or make proteins. Although they still have some specific proteins (P-proteins – apparently previously known as ‘slime’!^ref), mitochondria, endoplasmic reticulum, and sieve element plastids.^ref Both types of sieve cells have helper cells alongside which metabolise on their behalf – companion cells in angiosperms and Strasburger cells in gymnosperms.

Since phloem is full of delicious sugar-rich fluid, it can be a magnet for insects, which in turn introduce microbial pathogens including bacteria and viruses.^ref Plants produce metabolites to defend themselves against these pathogens, and also induce sieve plate occlusion – basically blocking up the sieve cell or tube where the pathogen is located to avoid it spreading.^ref

Both the active phloem and the old phloem which no longer transports photosynthates are together known as the inner bark. Outside these phloem layers is the ritidome or outer bark. You can read more about bark here.

For bonsai there’s really not a lot you need to worry about with respect to phloem, unless you are wiring super tight and cutting off the phloem (but by then your wire will be well embedded in the outer bark).

Biogold

Biogold is another popular bonsai fertiliser, which may or may not be cagey about its ingredients since the packaging is all in Japanese which I cannot read. Deploying google translate on their website, and searching online yielded some information:

It’s a fertiliser with N:P:K ratio NPK 5.5:6:3
It contains micronutrients iron 0.12%, copper 50mg/kg, molybdenum 27 mg/kg, sulfur 0.5% and also magnesium and calcium (in unspecified amounts)
It contains chicken manure fermented using bacterial processes

Chicken manure isn’t used directly on plants because the organic matter will ferment and generate heat, usually it is fermented separately along with plant matter such as straw, leaves, cardboard etc, and requires turning or mixing to ensure exposure to air (this is aerobic fermentation which requires oxygen).

So it’s likely that Biogold contains some other kind of plant matter which is unspecified. When looking at other products, plant matter (particularly green or coloured leaves or skins) provided substances which helped the microbial communities in the soil flourish, enhancing root growth and nitrogen uptake. One study found a “positive effect of BioGold® and Compost in increasing the soil microbial population by providing nutritive sources for the growth of soil microbes”^ref

Chicken manure is a good source of nitrogen, contains humic acid^ref, which is a concentrated form of organic matter (also contained in the coal precursors leonardite and peat), and was found to have better growth potential for plants than cow manure^.ref

A researcher growing coconut compared BioGold with other fertilisers in this study^ref – and found “There were no significant differences (P> 0.005) between treatments in any of the growth parameters tested after a period of six months after planting.” ie. the plants tested had similar outcomes from all the fertilisers tested (which included inorganic fertiliser, cattle manure, ‘Kochchikade biofertilizer’ and compost).

So overall, hard to say, this product appears to be a good fertiliser with micronutrients and humic acid/concentrated organic matter. But since it doesn’t disclose all the ingredients it’s impossible to fully assess it.

What is organic fertiliser?

The word ‘organic’ in terms of fertiliser does not mean the same thing as ‘organic’ when it comes to food.

Organic food follows principles of production which in general do not permit soluble fertilisers and synthetic pesticides^ref to be used during the food production.

Organic fertiliser means “any substance composed of animal or vegetable matter used alone or in combination with one or more nonsynthetically derived elements or compounds which are used for soil fertility and plant growth.”^ref This does not imply that the animal or vegetable matter itself was not produced using chemicals or is organic in a food sense.

As an example, rapeseed meal can be called organic fertiliser if the oil has been extracted using cold pressing methods, but this doesn’t mean that the rapeseed itself was grown using organic farming methods. If the oil has been extracted using a solvent, I think it’s doubtful that this rapeseed meal should be called organic.

Non-nutrient Additives

Like any hobby, the bonsai world has its share of fads, snake oil and quackery. None more so than in the multitude of different potions and elixirs offering to bring a bonsai to perfection, for the right (expensive) price. Amusingly, many of these go to great pains to emphasise that they are NOT fertilisers (since actually fertiliser is cheap and relatively easy to buy). Not only that, but many fail to include ingredient lists, reference real data or otherwise explain how their product is supposed to work.

Of course plants need nutrients, these are usually elements and explained in the post Nutrients for Trees. But there are a range of other ingredients which may or may not support your trees’ health, so I thought I’d start a list to help you work out what a product might be seeking to achieve:

Blood meal – eugh! A non-ethical source of nitrogen. There really is no need to use animal blood when you can get nitrogen from any rotting organic matter/compost.
Charcoal – in the form of biochar – depending on what it’s made from, helps water retention, attracts and provides a home for benefical microbes and provides nutrients & micronutrients (acts as a fertiliser)
Cocoa bean shell mulch – supports endomycorrhizae and nitrogen-fixing bacteria for root growth BUT also contains theobromine which is toxic to dogs, cats & fish
Conifer oils – tend to be antimicrobial, insect repellent, antifungal etc
Ectomycorrhizae and endomycorrhizae – fungi which interact with roots to improve uptake of nutrients – whether a particular species of tree uses endo or ecto mycorrhizae is detailed in this site.
Feather meal – another non-ethical source of nitrogen.
Flavanoids, flavanols, flavanol glycosides, anthocyanins – support the symbiosis between roots and arbuscular mycorrhizal fungi (a type of endomycorrhizae), as well as with nitrogen-fixing bacteria^ref
Humic acid – ultra-dense organic matter, converts elements into forms available to plants^ref, nourishes microorganisms in the soil and may mimic the phytohormone auxin
Japanese Cedar (Cryptomeria japonica) oil – insect repellent, insecticide, antifungal, antimicrobial
Japanese Cypress (Chamaecyparis obtusa) oil – antibacterial, antifungal
Kaempferol – a flavonoid (see above)
Leonardite – source of humic acid (see above) – extracted via open-cut mines
Manure – animal manure is a source of organic matter; from omnivores (eating both plants and animals – eg. chickens or pigs) it is higher in total nitrogen and phosphorus than from herbivores (eating only plants – eg. horses, sheep or cows) which have manure higher in total carbon^ref
Pine oil – insecticide/insect repellent
Quercetin – a flavonoid (see above)
Saponin – an insect repellent
Seaweed – a fertiliser which includes micronutrients which don’t appear in standard fertilizer, such as sulphur, as well as plant metabolites which can support the growth of mycorrhizal fungi and nitrogen-fixing bacteria. Seaweed extracts have been known to promote plant growth.^ref
Succinic acid – helps reduce heavy metal contamination – as a component of Alar was used for improving fruit set in fruit tree (before Alar was banned as a carcinogen)
Vinasse – source of organic matter and potassium (can be chemically processed)

Read more about what some products contain here: HB-101 Analysis, SUPERthrive, Green Dream, Bioc h ar and Biogold.

Green Dream

Green Dream is one of those products that is spoken about in whispers as some kind of miracle elixir. It was created by UK bonsai artist Colin Lewis who now lives in the US – and sells the same product there from his website. In the UK it’s available from Kaizen Bonsai. So what’s in Green Dream? Let’s just say you don’t want to use this product if you are a vegetarian, vegan, or interested in animal welfare. In the FAQs on the UK supplier’s site, it lists the following:

Blood meal – a source of nitrogen. Personally I feel that animal blood is over the top when nitrogen can be found in compost or any other rotting organic matter. Most likely the blood is an abattoir side-product, and associated with animal cruelty.
Feather meal – also a source of nitrogen and a side-product of the poultry processing industry – not known for its animal welfare standards either.
Cocoa shells – are the husks from processing cacao beans for chocolate. In theory this might be positive for your trees since cocoa (and its shells – known as Cocoa Bean Shells or “CBS”) contain bioactive compounds such as polyphenols. The polyphenols in chocolate products “comprise mainly catechins, flavonol glycosides, anthocyanins and procyanidins”^ref – of these, flavonols and anthocyanins are both flavonoids, known to support the symbiosis of roots with arbuscular mycorrhizal fungi as well as nitrogen-fixing bacteria^ref
CBS also contain theobromine^ref, which is toxic to aquatic animals, cats and dogs at reasonably low levels, so please be careful if you are using this product where cats or dogs can access it.
Dried organic seaweed – since seaweed is a plant itself it contains all the nutrients plants require – including many of the micronutrients which don’t appear in standard fertilizer, such as sulphur, as well as plant metabolites which can support the growth of mycorrhizal fungi and nitrogen-fixing bacteria. Seaweed extracts have been known to promote plant growth.^ref
Vinasse – is the by-product of sugar ethanol production. It is a potassium source and a “soil fertility improver because it promotes deep root development, nutrient lixiviation and increases considerably the sugarcane yield”^ref however there has been controversy over its use due to environmental damage from the high organic content.^ref
Slow release compound fertiliser with an analysis of N.6% – P.5% – K.7%.
With added trace elements. Iron, Manganese, Zinc, Copper, Boron, Molybdenum (probably from the seaweed and vinasse)

Overall I won’t be using Green Dream Original as I am a vegetarian and don’t wish to use animal products from cruel farming practices for my bonsai. Also, I have a dog and don’t want to put him at risk.

The product is labelled as an organic fertiliser but this doesn’t mean its ingredients are organically produced in the same way as food: What is organic fertiliser?

In researching this article I also looked into another product on Kaizen Bonsai’s website – Green Dream Rapeseed Meal. Rapeseed is also known as canola, it’s a Brassica vegetable whose seeds are grown used for oil, which is used as vegetable oil in cooking, and as a biofuel^ref Since 28.3 million metric tons of rapeseed oil was produced worldwide in 2020/21^ref, there is a heck of a lot of rapeseed meal to dispose of! Rapeseed meal is used as an animal feed, due to its relatively high protein content, and traditionally was used in China as a fertilizer. This is probably because China is the second largest producer and consumer of rapeseed oil and so has a lot of meal.

The meal has plant nutrients in it, because it’s made from plants, you can see a full breakdown here. Aside from the NPK listed on the label, according to the Canola Council it also contains almost every other nutrient a plant needs (see Nutrients for Trees), except for boron and nickel, so a bit like seaweed this can provide some of the trace elements that aren’t always available in the soil or in standard fertilizers.

There is a research paper^ref breaking down the compounds found in rapeseed meal, of these only one has any known effect on plant growth and that’s kaempferol – we came across it over in the HB-101 Analysis – it encourages the growth of endomycorrhizal fungi which aid nutrient uptake in roots.

One thing to know about rapeseed meal is that when it’s not dressed up as a bonsai fertilizer, it can purchased for quite a bit less. I found 20kg available for less than £14 (including delivery to UK mainland) at this site selling animal feed.

Will water drops on my trees burn the leaves?

This is one you sometimes hear in gardening circles – that you might burn the leaves of your plants if you water them in the heat of the day – because the drops of water act as a magnifying glass, focusing the light onto the plant and theoretically burning it. I have never observed water-droplet-shaped burns on a leaf which one would expect from this kind of behaviour. But what does the science say?

This article^ref references another one behind a paywall which says that although droplets can increase light 20x at their focal points, in most of the species tested a layer of leaf trichomes hold droplets above the leaf surface, and beyond the focal point.

In another study^ref “sunlit water drops on horizontal leaves without waxy hairs cannot cause sunburn regardless of solar elevation and drop shape.” – this is because “the focal region of water drops falls far below the leaf at higher solar elevations and can fall on to the leaf only at lower solar elevations, when the intensity of light from the setting sun is generally too small to cause sunburn.”

Unfortunately both papers conflict somewhat as the first says trichomes specifically hold water droplets too far away from a leaf to enable sunburn, and the second paper says only horizontal ‘hairy leaves’ can get sunburn (they found this could happen for floating fern but this plant has quite specific trichomes/hairs). In reality most bonsai trees do not have horizontal leaves, instead leaves are at a multitude of angles, and the water droplets if stuck to a leaf would probably be angled away from the midday sun. But do send me a picture if you ever see a bonsai tree burned by a water droplet!

SUPERthrive

SUPERthrive is another product claiming great results for plant health without being a fertiliser. I’m not sure why these companies find it so offensive for their products to be known as fertilisers! Fertiliser just means a product containing plant nutrients. Anyway, what is in SUPERthrive? Here is the ingredient list:

So to start with – it *is* a fertiliser (1:1:1). Aside from nitrogen, phosphorus and potassium it also contains another macronutrient – calcium, and a micronutrient – iron. I’ve taken the explanation of these below from my post What each nutrient does (x17).

Calcium is used for plant structure as it strengthens the cell walls in plants. Its presence (or absence) is also used for signalling of stresses to the plant, allowing it to activate defences against pathogens. There is twice as much calcium in this product than N P or K – so quite a lot.

Iron is present in a large number of different enzymes within plant cells, appearing in chloroplasts (where photosynthesis takes place), mitochondria (where energy is created) and the cell compartment. Iron is therefore a key nutrient for growth and survival in plants – in just the same way it is with humans and other forms of life. Iron is a component of so many enzymes that there is a specific name for them – ‘FeRE’ or iron requiring enzymes (Fe is the chemical symbol for iron).

Iron can be toxic if too much is present, so plants have evolved mechanisms to remove it when it gets too high. There is a much smaller amount of iron than other nutrients in SUPERthrive.

SUPERthrive also contains four varieties of mycorrhizae (fungus which integrates with plant roots). The types included are all arbuscular mycorrhizal fungi which are a form of endomycorrhizae – that is, the fungal cells enter the plant’s roots. This supports healthy root development, improved access to soil nutrients and healthier trees. You can find these mycorrhizae in soil, particularly in established forests. Whether or not a specific type of mycorrhizal fungus will benefit your tree depends on the species of tree. There is a list of which types work with with species on this site.

From a bonsai point of view this list helps us see that endomycorrhizae (ie. the fungi in SUPERthrive) are not associated with plants in the families Pinaceae (fir, cedar, larch, spruce, pine, hemlock) and Fagaceae (beech, chestnut, oak), neither should they work for lime trees (Tilia).

They are associated with plants in the families Cupressaceae (cypress, juniper, redwoods, thuja), as well as acers, ginkgos and most other flowering trees. So you might see a difference in effect depending on the species of tree with which you use this product.

The final ingredient in SUPERthrive is humic acid. Leonardite, the source of the humic acid in this product, “is an oxidized form of lignite, very enriched in HS [humic substances] and characterized by well-known auxin-like effects”^ref Lignite is a form of brown coal, which used to be peat but hasn’t become coal yet. Humic acid is a liquid made by dissolving leonardite, so it contains dissolved, concentrated organic matter (dead plants), effectively this is like super-concentrated liquid compost. Could it be similar to compost tea? In fact, yes, liquid from compost has also shown the same auxin-like effect^ref. Peat analysis shows a chemical composition of carbon, oxygen, hydrogen, nitrogen, sulphur in decreasing order.^ref But this doesn’t tell the whole story. Peat and its compressed descendants contain a multiplicity of nutrients as well as other components – basically it’s all the ingredients which go into plants, and are synthesised by plants, compressed and starting to decompose. So this component of SUPERthrive probably has most of the nutrients required for plant growth – although these aren’t necessarily bioavailable. This study found that “Leonardites did not affect significantly any measured variables in comparison to the control”^ref So my guess is that if you are fertilising your trees with a comprehensive fertiliser, and giving them some organic matter, the addition of humic acid may not make a difference.

Leonardite is mined in open-cut mines, and can be extracted using chemicals, so it’s not particularly environmentally friendly^ref, nor sustainable as claimed by this manufacturer^ref, since it takes 300 million years to create!

Ultimately this product is a fertiliser with extra calcium, mycorrhizae to promote healthy root development (but only for certain tree species), and concentrated liquid compost/organic matter. It probably provides beneficial compounds to bonsai trees – particularly those in families which benefit from endomycorrhizal fungae. But I’d argue these compounds could be obtained elsewhere – from a comprehensive fertiliser, compost tea and a handful of humus (dark, organic material that forms in soil when plant matter decays) from your local forest. It’s probably a useful product though if you don’t have the time or access to other additives for your bonsai.

HB-101 Analysis

Recently a member of my bonsai club was talking about this product, HB-101. It is apparently wildly popular in Japan and supposed to be fantastic for bonsai. It claims to be an “all-purpose natural plant vitalizer”. Since plants synthesise their own requirements for growth from the 17 nutrients, I couldn’t really see how this would work unless this product was a fertilizer, so wanted to dive a bit deeper into this product to work out what it does. Unfortunately the product website is pretty waffly, or possibly just poorly translated, so a bit of investigation was required.

According to the manufacturer HB-101 is made from “essences of such long-lived trees as cedars, Japanese cypress, and pines as well as from plantains.” Without knowing how they define ‘essences’ and which bit of the plantain they use, this doesn’t help much. But more info is in their submission to the United Nations Industrial Development Organisation: “HB-101 is synthesized from organic distillate, which is extracted from the heated raw material of cedars, Japanese cypress, pines, and plantains as raw materials”. So it contains substances from Cryptomeria japonica (Japanese Cedar), Chamaecyparis obtusa (Japanese Cypress) and Pinus thunbergii (Japanese Pine) as well as plantain grass (not plantains like bananas).

In their safety data sheet it shows the product has a pH: 3.0 ~ 4.5, and is toxic to fish, daphnia and other aquatic invertebrates within 48h at 1% concentration or more. The product explanation from the UN submission contains more useful data including a typical analysis chemical breakdown:

Kaempferol; 0.1 ~ 0.2 ppm
Water-Soluble Nitrogen (as N); 0.001 ~ 0.005 %,
Water-Soluble Phosphoric Acid (as P₂O₅); 0.0001~ 0.0005 %,
Water-Soluble Potassium (as K₂O); 0.0001 ~ 0.0005 %,
Total Sulfur (as S); 0.0001 ~ 0.001 %,
Calcium (Ca); 0.5 ~ 3 ppm,
Magnesium (Mg); 0.3 ~ 3 ppm,
Iron (Fe); 0.01 ~ 0.05 ppm,
Zinc (Zn); 0.01 ~ 0.05 ppm,
Silicon (Si); 1 ~ 5 ppm

Based on this breakdown, the product appears to be mainly a nitrogen fertilizer (NPK of 10:1:1) which includes all six macronutrients (nitrogen, phosphorus, sulphur, potassium, magnesium, calcium), and two micronutrients (zinc, iron). It also contains two non-nutrient ingredients – silicon and Kaempferol.

I was surprised to see silicon in the list as it’s not considered one of the 17 required plant nutrients. But a bit of digging and apparently it “activates plant defence mechanisms” and “increases the resistance of plants to pathogenic fungi”^ref. Interesting! Looks like I will need to write a new post on non-essential-but-benefical nutrients…there are bound to be others aside from silicon.

The other ingredient is Kaempferol. Kaempferol (in case you were wondering) is a flavonoid (substance synthesised by plants) which “has a role as an antibacterial agent, a plant metabolite, a human xenobiotic metabolite, a human urinary metabolite, a human blood serum metabolite and a geroprotector.”^ref It has a molecular formula of C₁₅H₁₀O₆. Flavonoids are “pigments that color most flowers, fruits, and seeds”^ref and they are actually produced by plants themselves, so it’s not obvious to me why adding them to a plant would do anything.

The product explanation claims that Kaempferol ‘activates plant mitochondrial enzymes’. Looking into Kaempferol further, it is referenced in a wide variety of human disease research, including cancer^ref and brain injuries^ref. It does indeed appear to affect the function of mitochondria and provide protection to cells against injury – at least in humans. In this article Kaempferol is said to protect against oxidative stress and various forms of toxicity by affecting mitopaghy (the removal of damaged mitochondria), suppressing fission (cell reproduction) and apostosis (cell death). In humans it seems to have the almost magical property of helping healthy cells to survive while inducing the death of cancer cells^ref.

Admittedly plants (like all complex life) do contain mitochondria, which generate the energy needed to power cells. So if a substance affects mitochondria in people, it may well have similar effects in plants. The question is whether externally delivered Kaempferol can actually enter the plant and get into its cells, which it would need to do in order to make any difference. As flavonoids are synthesised by plants, and since plants don’t absorb this kind of substance – instead absorbing the raw materials to make it themselves – I don’t think Kaempferol can be having any impact on the plant mitochondria.

BUT – what it might be doing is having an effect on other living things that affect tree health. And hey presto, a bit of searching uncovered that Kaempferol has been shown to improve root development by supporting Arbuscular Mycorrhizal Fungi (AMF) ^ref – this is a type of fungi in soil which can help expand the volume of soil from which nutrients can be extracted (Thomas).

In one study a range of flavonols were tested for their contribution to the growth of mycorrhizal fungi and Kaempferol was shown to make a modest improvement^ref but another flavonoid called Quercetin was even better.

Kaempferol does come from conifers which are in this product’s ingredient list. But it’s also high in green leafy vegetables like spinach, kale and dill^ref. So my guess is that a lot of it comes from the plantain grass in this product. Quercetin, which was more effective for nurturing mycorrhizal fungi, is apparently found in red, green, and purple-pigmented plants – for example, red onions. Unfortunately though, it seems that Quercetin (and Kaempferol) are not very easy to extract – industrial methods (likely the one used for HB-101) require ethanol but if you’re keen here is a method using ‘subcritical water’ (liquid water under pressure at temperatures above usual boiling point, 100 °C (212 °F)

So what else might the cypress, pine and cryptomeria be contributing? The company’s product page gives a few other clues – specifically it mentions saponin, pine oil and succinic acid, although these are not listed on the chemical analysis data sheet.

Saponins are substances produced by plants which are “responsible for plant defense against antagonists; such as mollusks, pathogens and insects”^ref They are contained in a wide range of plants but do not appear to be present in conifers^ref. By contrast saponins are found in plantain grass (and actual plantains!)

Looking at what the conifers are providing to this product – pine oil has larvicidal and mosquito repellent properties^ref, Cryptomeria japonica oil is insect repellant and insecticidal^ref, antifungal against tree pathogenic fungi^ref as well as antimicrobial^ref and Japanese Cypress oil is antibacterial and antifungal^ref (and apparently also good for hair loss!).

And finally, succinic acid. This has been shown to improve tree tolerance (in Larix olgensis) to heavy metal contamination – specifically with Lead^ref and Cadmium^ref. This doesn’t seem to me a particularly useful attribute for bonsai, since we’re using inert bonsai medium. Dig a bit further and you find succinic acid was combined with 2,2-dimethylhydrazine to make a plant growth regulator called Daminozide (also known as Alar). It regulated the growth and set of fruit but has been banned due to concerns about cancer risk. This isn’t on the ingredient list so I don’t think it’s present in the product. I can’t find much useful information on what succinic acid might be contributing.

So what’s my overall analysis? Initially I was sceptical because I don’t like products that rely on fluffy advertising and don’t explain how they work. It annoyed me that the product doesn’t contain an ingredient list, and it doesn’t admit to largely being a fertiliser, which is most definitely is.

However one of the key features of this product is that parts of it are derived from a distillation process, which enables the extraction of beneficial compounds from the conifer leaves and wood as well as from the leafy plantain grass. These should help boost a tree’s defences to insects, pathogenic microbes and fungi, and improve the mycorrhizal activity in the pot to supports better root development (and thus healthier trees). It also has a lot of nitrogen, which as outlined in nutrients is hard for plants to obtain.

So somewhat grudgingly I have to say it might actually work.

Photosynthesis

Another epic topic which has occupied scientists for the best part of 400 years, the equation for photosynthesis itself was not understood until the 1930s.^ref

Photosynthesis is the process of turning energy from sunlight into chemical energy, a process which famously is performed by plants, specifically by plant cells containing ‘chloroplasts’. Chloroplasts contain a substance called chlorophyll. Chlorophyll is often described as a ‘pigment’ – but this makes it sound like its only role is to colour things green! Which of course it isn’t – being green is just a result of its real function which is to absorb sunlight of a certain spectrum. Chlorophyll absorbs visible light in two regions, a blue band at around 430 nanometers and a red band around 680 – according to Vogel. Other sources state the bands are 680 nm and 700 nm^ref. Everything else is reflected, which looks green. Chloroplasts are believed to have originally been cyanobacteria which were incorporated into plant cells to provide photosynthetic capability (Lane, 2005). To see where chloroplasts and chlorophyll are present within a leaf, check out this post on leaf structure.

The sequence of reactions which happen during photosynthesis are known as the Calvin-Benson-Bassham cycle, after the scientists who discovered it. The simplified equation describing photosynthesis is as follows:
6CO₂ + 6H₂O –light energy–> C₆H₁₂O₆ + 6O₂.

This suggests that photosynthesis is the exact opposite of respiration, creating glucose instead of consuming it. But actually this equation is incorrect as photosynthesis does not create glucose. The Calvin et al cycle produces a molecule called G3P which is a 3 carbon sugar which can be used to create other molecules. Anyway, that’s probably not super-relevant for bonsai! The main insight from the equation above is that light energy is needed for plant survival and growth – this is why trees do not like being inside unless they have a suitable artificial light source.

Another point to note is that plant cells, like all living cells, respire. Plant cell respiration is like animal respiration, that is, cells consume oxygen and glucose to produce energy, while emitting carbon dioxide and water. Cells use respiration to generate the energy they need for metabolism (basically, keeping the cell alive and functioning). All cells in a tree respire, including the leaves, roots and stems, 24 hours a day. This means trees offset some of their photosynthesis by respiring – in particular at night when no photosynthesis occurs.

On balance, leaves produce a lot more sugars and oxygen through photosynthesis than they use during respiration – and this provides the energy they need to maintain themselves and grow. In fact the point at which they *don’t* produce more than they use through respiration is as low as 1% of full sunlight (Vogel). Note that this low level can be reached if a leaf is entirely shaded by 2 other leaves, since the typical light transmission through a leaf is only 5%.

Another interesting fact about photosynthesis is that leaves can only use about 20% of full sunlight before the photosynthetic system saturates (Vogel). This number actually varies depending on the species and leaf type. So leaves below the top layer (likely to be ‘shade leaves’ described in this post: Leaves) can still get enough light from partial exposure, if they are slightly shaded or lit for only part of the day, to saturate and max out their photosynthetic capability. The majority (99%) of the energy absorbed is used to maintain the leaf itself, so only 1% is released for growth.

But – back to the photosynthesis equation – which is an extremely simplified version of what is actually happening. Photosynthesis requires 150 discrete steps involving a similar number of genes^ref. A good reference is this Nature article.

Photosynthesis takes place in two stages. First the ‘light dependent’ reactions happen. Light energizes electrons within the chlorophyll, and these electrons are harnessed to produce ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) which are molecules used by cells for energy and as an electron source. The chlorophyll replaces its lost electrons by taking some from water – effectively they ‘burn’ or oxidise water, leaving the oxygen behind as a waste product (Al-Khalili).

After this the ‘light independent’ reactions happen. These are facilitated (sped up) by an enzyme known as RuBisCO. Using the energy sources created in the first step (ATP and NADPH), RuBisCO ‘bolts’ together the hydrogen from the water, and the carbon and oxygens atom from the carbon dioxide, along with phosphorus, to make the 3 carbon sugar glyceraldehyde-3-phosphate (C₃H₇O₇P) (Lane, 2005). This is known as carbon fixation.

In reality there is also a third stage where the ingredients for the cycle are regenerated so that it can continue running.

The full equation (the Calvin-Benson-Bassham cycle) – is:
3 CO₂ + 6 NADPH + 6 H⁺ + 9 ATP + 5 H₂O → C₃H₇O₇P + 6 NADP⁺ + 9 ADP + 8 P_i
(P_i = inorganic phosphate, C₃H₇O₇P = glyceraldehyde-3-phosphate or G3P)

Sorry for geeking out for a minute there!

An important point is that photosynthesis doesn’t just go up with increasing sunlight, it has a set of limiting factors which were described by Blackman in 1905 in his article^ref “Optima and Limiting Factors”. He said “When a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the slowest”. The limiting factors he described for photosynthesis included light intensity, carbon dioxide and water availability, the amount of chlorophyll and the temperature in the chloroplast.

The amount of sun needed to max out photosynthesis from a light intensity point of view is not as high as you would imagine. Vogel says a leaf “absorbs about 1000W per square metre from an overhead sun shining through a clear sky” and photosynthesis only consumes 5% of this – 50W per square metre. Obviously this is going to vary depending on the species and whether a leaf is a sun leaf or a shade leaf.

But what does it mean for bonsai? Well – you might have spotted some other elements in the photosynthesis equation. NADPH (formula C₂₁H₂₉N₇O₁₇P₃) contains nitrogen and phosphorus, as does ATP (formula C₁₀H₁₆N₅O₁₃P₃). RuBisCO relies on a magnesium ion to perform its role as a catalyst. There are a bunch of other enzymes and co-factors which are required to support photosynthetic reactions as well – which explains why certain nutrients (including Nitrogen, Phosphorus, Magnesium, Potassium, Chlorine, Copper, Manganese and Zinc) are critical for trees in varying amounts – more here: Nutrients for Trees.

And if you’re concerned about whether your trees have enough light for photosynthesis, you can see exactly how much energy is arriving on your outside bonsai at this site. Find your location and download the PDF report and you’ll see the irradiation levels – which can be useful in understanding how your bonsai trees will fare. As an example, the max in my location is 328Wh/m² in April which explains why the olive trees in London are so unhappy looking – if you look at irradiance in Greece, where they thrive, it barely ever goes under 328Wh/m² even in winter! Trees in Greece receive nearly double the amount of irradiance than those in South West London.

One final point of interest with admittedly little relevance to bonsai – some plants (nineteen different plant families, independently of each other) evolved an improved photosynthetic process which is known as C4 photosynthesis. This concentrates CO₂ nearer to the RuBisCO enzyme, reducing its error rate. Unfortunately most trees use C3 photosynthesis with its associated inefficiency – other than Euphorbia, which are apparently “exceptional in how they have circumvented every potential barrier to the rare C₄ tree lifeform”^ref.