Tag Archives: Nutrients

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 effectref. 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 friendlyref, nor sustainable as claimed by this manufacturerref, 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 cancerref and brain injuriesref. 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 cellsref.

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 improvementref 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 dillref. 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 conifersref. 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 propertiesref, Cryptomeria japonica oil is insect repellant and insecticidalref, antifungal against tree pathogenic fungiref as well as antimicrobialref and Japanese Cypress oil is antibacterial and antifungalref (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 Leadref and Cadmiumref. 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 nmref. 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 genesref. 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 Pi   
(Pi = 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 articleref “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.

What each nutrient does (x17)

Understanding the exact role of individual plant nutrients is actually quite complicated. This is because many nutrients have multiple roles, and research hasn’t always clearly identified each role. It’s also because nutrients don’t act on their own – they usually form part of a larger molecule, such as an enzyme, and they usually interact with other nutrients, molecules and environmental factors such as pH. Then it requires diving deep to the molecular level to work out how chemical reactions take place and even how individual electrons move in the presence of the enzyme. I’ve read a bunch of papers and articles about the nutrients below but there is sure to be more out there – consider this a taster.

Macronutrients

Macronutrients are those inputs which plants require in substantial volumes in order to grow and metabolise. There are six macronutrients, of which three are metals.

1. Nitrogen: nitrogen is needed by plants for various reasons but one of the most important is for photosynthesis. Nitrogen is a component of chlorophyll, the green pigment in leaves which absorbs the energy from sunlight to break apart water in the photosynthesis reaction. The chemical formula of chlorophyll is C₅₅H₇₂O₅N₄Mg – as you can see both nitrogen and magnesium are needed in addition to carbon, hydrogen and oxygen which is obtained from air and water.

Secondly, nitrogen is a key component of amino acids, which are used in all living things to make proteins. There are 21 amino acids in plants which are connected together in a myriad of different sequences and shapes to make the different proteins. Examples of plant proteins include the storage material in seeds and tubers, plant cell membranes and the enzyme known as RuBisCO. RuBisCO is present in leaf cells alongside chlorophyll, and enables carbon fixation during photosynthesis – it is said to be the most abundant protein on Earth and represents 20-30% of total leaf nitrogenref. So photosynthesis requires chlorophyll and RuBisCO, both of which rely on nitrogen as a component element.

Finally nitrogen is present in the four bases used to create DNA (adenine, thymine, guanine & cytosine) and RNA (adenine, urasil, guanine & cytosine) which enables cell replicationref.

Nitrogen needs to be in soluble form to be used by plants, either as nitrate or ammonium, which requires the presence of specific bacteria either in the soil or in the plant’s roots. As I mentioned in my first post about nutrients, Hallé states that obtaining nitrogen is a constant challenge for plants. This is why the fertiliser industry is so prosperous – but unfortunately also so damaging for the environment. The Haber-Bosch process used to make Ammonia (NH3) is “one of the largest global energy consumers and greenhouse gas emitters, responsible for 1.2% of the global anthropogenic CO2 emissions”ref and nitrate runoff from highly fertilised fields damages rivers and ecosystems.ref The natural world has some clever ways to make nitrogen accessible – some plants incorporate bacteria into their roots which can do this, and in old growth Douglas fir forests, lichen in the canopy which contain cyanobacteria capture nitrogen from the atmosphere and when they fall to the forest floor they rot into components which trees can access (Preston, ‘The Wild Trees’). Similarly a relatively sustainable source of nitrogen for plants is rotting organic matter (along with the necessary microbes) – compost and manure are good options.

2. Phosphorus is needed in plants – and in fact in most living things – because it’s a key component of the molecule used to store, transport and release energy in cells. That molecule is called adenosine triphosphate (“ATP”) and it’s created during photosynthesis by adding a phosphorus atom to adenosine diphosphate. The ATP can then be transported throughout the organism to be used where energy is required, at which point it’s converted to ADP (adenosine diphosphate) which releases energy back to the cell. Phosphorus also provides the structural support for DNA and RNA molecules, needed for cell replication.

For plants phosphorus is fundamental to photosynthesis, as a phosphorus-containing substance called RuBP (C5H12O11P2) is used to regulate the action of RuBisCO in fixing carbon from carbon dioxide.

Phosphorus is a key part of most fertilizers and manure is a good sourceref.

3. Sulphur is a constituent of two amino acids – methionine and cysteine. Cysteine is used to create methionine as well as glutathione, an anti-oxidant which helps plants defend themselves against environmental stressref. Methionine is involved in cell metabolism and the majority of its use in the cell is to synthesise ‘AdoMet’ which is used in methylation reactions (such as DNA methylation which regulates gene expression) and to create the plant growth regulator ethyleneref.

Manure is a source of sulphur for plants.

Metals

In addition to the top three outlined above, it turns out that plants need some atoms of various metals as well. In order to understand why, we need to know that plant cells are full of chemical reactions which perform all the different functions required for metabolism. Helping these chemical reactions along are a type of protein known as enzymes. Enzymes act as a catalyst to chemical reactions in cells, speeding them up without consuming the enzyme material itself. Some enzymes have metal ions at their heart which assist the reaction (called ‘co-factors’) and these play a critical role in the enzyme’s function (for example magnesium is used in RuBisCO).

Three of the six macronutrients needed by plants are metals – potassium, calcium and magnesium.

4. Potassium is one of the three major macronutrients usually found in NPK garden fertilisers (K is the chemical symbol for potassium), reflecting its important role across several different dimensions of plant growth. One important role is in the production of proteins. As outlined above, proteins make up a large part of plant biomass, and the key protein RuBisCO is necessary for photosynthesis. Proteins are manufactured on structures called ribosomes within the cell – and ribosomes need potassium in order to do their jobref.

The other important role for potassium is in providing the pressure within plant cells which keep them stiff and ‘turgid’ – without it they would become flaccid and the plant would fall over. The manipulation of turgidity within leaves is one way a plant controls the level of air coming into the leaf – to close off the air holes (stomata) the guard cells around the stomata are made more turgid which closes the gap between them. Potassium is involved in this process.

In nature the main source of potassium is the weathering of rocks, but it’s also contained in organic matter, particularly in seaweed.

5. Magnesium is a component of the chlorophyll molecule and is key to the operation of RuBisCO, both of which enable photosynthesis. It is found in soil from the weathering of magnesium-containing minerals – the University of Minnesota recommends dolomitic limestone or tap waterref.

6. Calcium isn’t just used for human skeletons, it’s also 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. Sources of calcium for gardening include lime or shells.ref

Micronutrients

Micronutrients are required in much smaller amounts than macronutrients, although they are still required.

7. Boron appears to have been identified as a plant micronutrient mainly due to the effects of not having enough of it, with researchers having observed that boron deficiency leads to root, leaf, flower, and meristem defects. The precise role that boron plays is not easy to find in the literature, other than it being generally agreed to be important as a structural component of the plant cell wall, helping to provide rigidityref. Boron also appears to be required for reproduction, and a lack of it can affect pollen germination, flowering and fruiting. Because boron has poor mobility in a plant and cannot be moved from one part of the plant to another, continued exposure to it is needed in order to avoid a deficiency – but the exact levels vary widely by plant.

Sources of boron include borax (sodium borate) but since boron toxicity is apparently possible at high levels be very careful with this approach. Obtaining boron from organic matter or liquid seaweed instead may be less risky.

8. Chlorine was added to the plant micronutrient list in 1946 since it was found that chlorine molecules are required as part of the machinery of photosynthesis – particularly relating to the water-splitting system. In addition to this essential function, chlorine has also been found to be beneficial at macronutrient levels, enabling “increased fresh and dry biomass, greater leaf expansion, increased elongation of leaf and root cells”ref.

Since most people will be using tap water for watering their bonsai, getting adequate chlorine to your trees should not be a problem, but if you are using rainwater perhaps consider tap water every now and then.

9. Copper is essential for plants because along with iron it makes up part of an enzyme called cytochrome oxidase which performs the last of a sequence of steps in respirationref. Cytochrome oxidase is present in the mitochondria of plant cells – these are separate organelles with their own unique DNA which are dedicated to energy production. Copper is also found in plastocyanin, a protein which is responsible for electron transfer in the thykaloid – the light-dependent part of the chloroplastref. This protein is key to the conversion of light energy to chemical energy in the cell during photosynthesis. Copper is found in the soil but apparently is deficient in soils with high amounts of organic matterref.

10. 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. ref1 ref2 ref3

11. Manganese is also a co-factor to enzymes involved in photosynthesis, as part of the ‘oxygen-evolving complex’ in photosystem II, which contains 4 manganese ions. Photosystem II “is the part of the photosynthetic apparatus that uses light energy to split water releasing oxygen, protons and electrons”ref.

12. Molybdenum is used by certain enzymes to carry out redox reactions (reactions where electrons are gained or lost from a molecule); these include nitrate reductase, xanthine dehydrogenase, aldehyde oxidase and sulfite oxidaseref. Its role facilitating the nitrogen pathway in a plant is important since nitrogen is the nutrient plants require the most of, and the presence (or absence) of molybdenum can make a big difference to the efficiency of nitrogen uptake which in turn affects growth rates and plant health.

13. Nickel is a co-factor to the enzyme urease which breaks down potentially toxic urea (a product of metabolism) into ammonia which can then be used as a source of nitrogen for the plantref.

14. Zinc is the final micronutrient alphabetically but not in terms of importance. It is associated with 10% of all proteins in eukaryotic cells including those of plants, assisting as a co-factor to many enzymes and so enabling many different biological processes including transcription, translation, photosynthesis, and the metabolism of reactive oxygen species. Zinc also plays a role in ensuring the correct folding pattern for proteins as they are created.ref

Interestingly, zinc deficiency is associated with smaller leaves and internodes, which you might consider a benefit for bonsai, but perhaps not at the expense of your trees’ core biological processes!

Wait – I only got to 14 and there are supposed to be 17 – what the heck? Oh yeah – here they are (15) carbon and (16) oxygen from carbon dioxide, and (17) hydrogen from water (H2O). Did you know that the oxygen emitted from plant photosynthesis actually comes from the water and not from the carbon dioxide? More in Photosynthesis.

Nutrients for Trees

Before we dive into this subject, it’s important to know there are two aspects of ‘feeding’ trees and the one we are going to cover in this article relates to the nutrients that plants need in order to generate new cells and growth.

The other aspect relates to the nutrients which can contribute to a better growing environment for the plant – for example, increasing mycorrhizal fungi, reducing pathogens, and improving the community of bacteria interacting with the roots of the plant. You can read about those in Non-nutrient Additives.

In general true nutrients – as they are referred to in the literature – are elements – ie. they are not able to be decomposed into smaller components, and you will find them all listed on the periodic table of elements. There are 17 elements which are recognised as plant nutrients, and from these trees synthesise their own biomass as well as everything that’s needed to make it (like secondary metabolites, enzymes, carbohydrates, plants produce literally thousands of compounds).

Three of the required elements are derived from air and water (oxygen, carbon and hydrogen). Of the remaining 14, there are six macronutrients (present in higher volumes) and eight micronutrients (required in smaller amounts).

This is important for bonsai because trees usually obtain all of their nutrients from air, water or soil. Since bonsai are not planted in soil, they are vulnerable to nutrient deficiencies. To learn more about how trees absorb nutrients, check out how roots absorb water & nutrients. For a description of each nutrient, why it’s needed and how it’s obtained by plants when not in a pot, please read the post on what each nutrient does. If you don’t want the detail, below is the (relatively) short version…

There are two ways in which nutrients are used by a plant and these relate to what the tree is, and what it does.

What are trees made of?

The main structural components of trees are lignin and carbohydrates. Lignin is a polymer which combines three types of alcohol (p-coumaryl, coniferyl & sinapyl) in different ways, which in turn combines with cellulose (a carbohydrate) to form wood. Lignin makes up 25–35% in gymnospermsref and 20–25% in angiosperms, cellulose makes up most of the rest, with 4-10% of other components. Whole text books have been written just on the topic of lignin and it isn’t fully understood as a substance – it could be considered the ‘secret sauce’ to tree success. Feel free to spend $183ref to learn more…or buy another nice tree instead!

Both lignin and cellulose are made up of carbon, hydrogen and oxygen, all of which is obtained from air & water through photosynthesis.

What do trees need to function?

A tree can’t become a tree with just carbon, oxygen and hydrogen, even though those elements make up most of its structure. It needs chemical reactions to take place throughout its life to create the cellulose and lignin, and to manage all of the processes needed to maintain life. This is why it needs other elements in addition to C, O & H.

Key reactions within a tree include photosynthesis, nitrogen capture, cell division and defence against pathogens – but there are millions of chemical reactions going on inside a tree at any given time. Many of these depend on enzymes, a type of protein which acts as a catalyst – that is, it enables something to happen without being consumed by the reaction itself.

As a protein, enzymes are made up of amino acids, which all contain carbon, hydrogen, oxygen, nitrogen and (sometimes) sulphur. This is where the first two nutrients come in – nitrogen is needed in every enzyme, and sulphur is needed in some.

Enzymes are really interesting because they don’t just make reactions happen, they also speed them up in really clever ways (to learn more see Jim Al-Khalili’s book Life on the Edge: The Coming of Age of Quantum Biologyref). To do this, they use other elements, including metals like potassium, iron, copper, manganese, magnesium, nickel & zinc. Boron, chlorine and molybdenum are non-metal enzyme co-factors (elements which enable enzymes to function).

The remaining two nutrients are calcium and phosphorus. Calcium is used by plants in a similar way to humans, as calcium pectate it acts as a skeleton, strengthening cell walls. It also acts as a chemical messenger as part of processes related to root and bud growth and responding to stress. Phosphorus has multiple roles, as a component of the molecule ATP (adenosine triphosphate) which is used by all living things to store and transfer energy, as the structural framework for DNA & RNA and as part of the carbon fixation process.

How to obtain nutrients for trees?

So we know that plants need significant levels of nitrogen, phosphorus, sulphur, potassium, calcium and magnesium and they also need smaller amounts of boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc. According to Hallé in his absolutely brilliant book ‘In Praise of Plants’, Nitrogen is a key limiting nutrient for plants. He says “Although they easily assimilate carbon, nitrogen remains a constant problem for plants. It is the reason that they are poor in proteins and rich in carbohydrates. The situation is the opposite in animals…”

Standard non-organic fertiliser does not contain all of these nutrients, so you need to make sure they are added somehow – either via an organic fertiliser or a combination of additives like liquid seaweed, compost or fermented/decomposed manure. Take care you understand what the definition of an organic fertiliser actually is. Unfortunately most fertilisers do not reveal their composition on their packaging, so look for one which does. My personal investment in fertiliser is my purchase of a Hotbin hot composting bin – this creates organic compost in 3 months and produces leachate which can be used as a liquid fertiliser. Also consider your carbon footprint. As mentioned in the what each nutrient does post, Ammonia production for chemical fertilizers is a major contributor to global warming as it uses fossil fuels as the main ingredient, as well as massive amounts of energy to produce, and contributes to ecosystem damage through nutrient runoff. Using compost with some manure is a more environmentally friendly way to provide nitrogen to your trees.

Consider your watering as well. Trees need *some* chlorine and grow better if they have a bit more than merely what they need – tap water can provide this nutrient if you use it for watering. You should check your local water company report as you may be able to obtain other nutrients from your water as well, including magnesium.

Whilst there are many research studies identifying the effects of nutrient deficiencies, there aren’t many with evidence for nutrient toxicity so it’s hard to work out if this is a myth or reality. Living things tend to have a system of homeostasis to manage levels of chemicals to avoid them getting too high (or low depending on the substance) so it may be that toxicity is rare due to homeostatic mechanisms removing excess nutrients.

Some bonsai practitioners are fans of foliar feeding. This can be useful in certain circumstances, but the better approach is to add nutrients to the soil.

How much is enough?

This is where the evidence starts to get very thin on the ground. Nutrient requirements vary between plant types and their ability to obtain nutrients is dynamic – it depends on the presence of other nutrients, temperature, pH, energy availability, the size of the plant – there are a lot of variables. Probably the best approach is to follow the guidance on the fertiliser you are using.

Reabsorption of Nutrients

A word of warning to those who like to remove those ‘messy’ dying leaves on deciduous trees at the end of the season. Towards the end of the growing season, once the tree has made enough wood and grown enough leaves, and, from the tree’s perspective, done everything it can to reproduce, it stops focusing on growth and goes into an orchestrated shutdown phase.

During this phase substances from the leaves are reabsorbed into the tree, to be stored in the rays and roots for use again next year – enzymes are again deployed to effect this absorption. This is why leaves change colour as different substances are reabsorbed. What is left in the leaf when it finally drops is actually quite low in nutrients. So let the tree drop its leaves as it wants, to optimise its health for next year.