Bonsai growth – Single Limiting Factors

I would like to share with you my thoughts on the implications of Limiting Factors for tree growth. The basic theory is that the optimum rate of growth of a bonsai will be limited by the one resource that is in the least supply. Obviously different trees require different balance of the essential factors but the basic theory remains. To recap the factors are water, light and the wide range of nutrients.

Leibigs Law “states that plant growth is limited by a single resource at any one time; only after that resource is increased to the point of sufficiency can another resource increase plant growth”*

We need to be mindful of this when choosing soils for re-potting, when watering and fertilising, and when choosing a place for our trees in the garden. For instance a light demanding tree can be well watered and fertilised but without adequate sun to photosynthesize, will always fall behind its own maximum potential.

It is interesting to see how plants respond to a Limiting Factor: “One of the major mechanisms by which plants adjust to resource imbalance is by allocating new biomass to the organs that acquire the most strongly limiting resource”*. This means that they can grow more leaf that root or vice verse – overall making the plant out of the balance that is so critical for quality bonsai.

Consider how a bonsai will respond to our attempts to improve growth with an oversupply of some nutrients without addressing the one that is missing. A plant will ‘spend’ Carbon to acquire Nitrogen and ‘spends’ Nitrogen to acquire Carbon. Essentially the plant can compensate to access the limiting factor, but again the cost is clearly a reduction from its maximum growth potential.

This was reinforced for me recently when I was fortunate enough to listen to an expert in hydroponics (the growing of plants without soil) speak and was very impressed with the results achieved by supplying the exact nutrient requirements of each species of plant (chemical analysis of leaves used to determine what the Limiting Factor was in each case).

One side effect is unexpected: “Individuals within a species tend to increase leaf and root longevity in response to nutrient stress.”* Starving a plant of some nutrients makes them tougher in the long term. I have been experimenting with this by holding back the Spring time feeding regime by a few extra weeks with the result so far showing no difference in tree health, and trees that (anecdotally so far) seem more resilient.

*All quotes taken from: Chapin, Bloom, Field, Waring (1987) Plant Response to Multiple Environmental Factors, Bioscience Vol.37 No.1

Oak Bonsai – how to make them drought tolerant

I have just been reading the latest scientific report on the development of cells in oak, and it is clear that there is some useful information here for Bonsai.

The research* suggests that trees which have abundant water when laying down earlywood (formed during the springtime flushing) causes the trees to create larger vessel diameter in the conductive tissue of the stem. Conversely less available water at this time causes a smaller diameter of vessel to form.

Later in the season the larger vessels need more water to fill them and to allow the natural transpiration process to ‘pull’ water up from the roots to the leaves, if the volume of water is not high enough them the leaves do not receive the water and will suffer scorch in hot sun. Smaller earlywood vessels need less water to active the ‘pump’ and can more efficiently provide water to the leaves, making them more drought tolerant in high summer.

So water less in spring and you will need to water less in summer.

However, the side effect of this is that for a tree in development we want the largest diameter growth on the stem and so can directly effect the annual increment by watering heavily in spring – more wood is created at this time than any other time of year as the late-wood (laid down in summer) is shown not to be effected by climatic conditions but by overall tree health.

Now the research paper was specifically on oak so I will have to find out if the same applies to other species, but it does seem to be a clever evolutionary trick, and I imagine similar mechanisms exist in other species.

Interesting stuff.

* Price (2015) Shake in Oak: an evidence review; Forestry Commission Research report

New series: why trees grow the way they do, a photo essay…. part one


I am a firm believer that if you understand how a tree grows naturally and then incorporate that into you Bonsai the final image will be inherently more convincing. I was reinforced in this view when an otherwise good tree was downgraded in judging because it looked like a Pine – the only problem was it was a Hawthorn!

So I want to talk about the differences between tree species. As this is quite a large topic I will break each blog into one key difference to help keep it simple – building up into a hopefully useful source of reference for everyone. So to begin:

What makes trees grow upwards?

Trees are fundamentally divided into two categories, they will either be Phototropic or Geotropic.

Phototropic trees are ones that are influenced by light. Trees need light to photosynthesize and any leaves that cost more energy to grow than they can produce are useless and the tree will shed them, if too many leaves are in the shade and get cast then eventually that branch will also be dropped. If the majority of light comes from one side then the tree will develop a bend or lean in that direction. Most broadleaved trees fall into this categoryP1000489. The photo shows one large old beech dominating a smaller one which has always grown under its canopy but with adequate side light to keep it alive, however it has developed a persistent angle of growth so it is now at 45 degrees, only eventually developing a more upright tip when out from under the crown of the dominant tree.

P1000500Geotropic trees are influenced by gravity. In any situation they will grow directly upwards. They can still loose branches if they don’t receive enough light but this can result in a straight tree with branches only on a single side. If a Geotropic tree gets blown over by the wind it will direct itself up again. Most conifers fit in this group.

Apologies for the poor photo here but if you look closely you can see that the stem blew over many years ago to lay along the floor, the angle of bend suggests that the now vertical stem was previously a branch, but as the closest part of the tree to vertical it has taken over as the leader, and then straightened to perfectly upright. A Phototropic tree in this situation would not have grown upwards but come towards the camera where the source of sunlight can be found.

To apply this to Bonsai a tree with a lean or twist needs it to be ‘explained’. Plantings involving more than one tree P1000493need to be consistent in how the trees interact. Look at this twin group, the tree on the right, if taken as a separate tree, would look ridiculous but when added together with its neighbour forms a single consistent canopy and looks interesting and acceptable, the deformation in the trunk and its one-sidedness is ‘explained’ by the dominant neighbour and can be enjoyed. Contrast this with a pair of Western Hemlock (below) just coming into bud. The photos show the overall image first, then a couple of angled shots to show how the large tree dominants the smaller one. Hemlock are strongly Geotropic so if I bent the trunk of the small one it would not have been ‘true’ instead it now gives the impression of having grown through the crown of the larger one, or the larger one over-topping the small one threateningly, or they coexist in harmony of mother embracing a child – you are left to choose, but you will not get distracted by a false image. These will rapidly fill out into a single canopy and start to look very interesting.

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If you still needed any convincing that a Bonsai tree needs to be grown to match its true nature, but think that maybe you could not really spot something that wasn’t true then take a look at these two photos and see which one strikes you as correct:

P1000491       P1000492

In each image, when you look at the small trees in the background as well as the large dominant trees in the foreground there are trees growing directly vertical and some that have a lean. So does your instinct tell you this is a flat site with leaning trees or a slope with vertical trees??? Answer in part two…

and don’t forget to check out the website at

Bonsai Forest from nursery stock


I was fortunate enough to be given a bundle of nursery planting stock. These are healthy young trees that have been grown to sold and planted out in the thousands so don’t have that degree of attention that bonsai seedlings would have lavished on them.These are cell grown Alder.

The trees are grown and delivered from the nursery in little plugs of soil so the roots are undisturbed during the transport and planting out, they come in wraps of 25 with a variety of degrees of sizes and shapes. As these are intended for the forest these small differences do not matter, however this difference can be exploited for a forest group planting.

Let’s see what we have as our Raw Bonsai material:


The first step is to sort out the sizes. I arrange them into Large (5 in number), Medium (7)  Small (10) and dead (3). Obviously the dead ones would not form part of the arrangement!!!

The large trees will form the central focal points and have already started branching. Medium trees will form a ring around these and the small trees, which seem to have already developed bends and twists in the trunks will be spread around the outer ring

The soil of the cells was loosened and any upward growing roots were removed, leaving any surface roots that will develop over time and be an attractive feature.

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Trying hard to hold the trees with one hand and take a photo with the other, it became impossible after this stage to take any more during photo’s so you will just have to fill in the gaps. The trees are sitting together in the pot but the roots are all separate and very easy to move about, also because the trees are cell grown then they can be turned individually to ensure that the natural shape of the stem is consistent with the overall image. Once the trees were in the correct placing the next step was to infill with bonsai soil, as this was pushed down it gripped the trees more and more firmly until they did not need to be held and the arrangement could take shape.

The trees are planted quite deeply at this stage. At the next repot, which could be as early as next year, the bottom layer 2cm of soil and roots will be cut off and the group can then go into a shallower wider pot more conventional for a forest planting, this pot is going to give the trees the best possible growth without allowing free running space for the roots

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And the finished group planting after a good amount of tweaking to give an outline of a forest grove. I will report back after the growing season to see the development.The photo tries to give a good silhouette of the final grouping. Some of the trees were pruned back to fit the outline, I have left the clippings which can be seen at the front of the photo.

I have tried to achieve a calm, balanced arrangement of stems, which will form a rounded dome very quickly. The growth habit of alder is to be tall thin trees, so the shape of the dome will ultimately reflect this. I have purposefully included some stems that cross low down, and some small stems at the back which run slightly against the natural flow in order to give it that little touch of imperfection, wabi-sabi, understanding of which is so important in appreciating bonsai.


Root structure from nature

Beech rootsReally great root structure is a difficult concept to get to grips with. Lots of advice can be found about root pruning at all stages of the bonsai life cycle, root grafting to fill in gaps on mature trees, growing trees on tiles in the ground in a  developmental stage to spread the roots, etc. That is all well and good but it is essential to keep in mind a natural image that we should be aiming for, like this Beech.

Also a neighbouring tree that blew down in the storms, but beautifully reveals the ramified root structure:


I also collected a few photos of some big old hedgebank beech trees. Hedgebanks are fairly beech in bankunique to the Westcountry and involve creating a bank of earth, laying a stone face over it and then planting a hedge on top – very secure against any sort of livestock and offers protection from the wind. Over the years these hedges don’t get cut and the hedge plants grow on to become trees, sometimes very substantial trees. The soil that was the bank slowly erodes over time in the wind and the rain and the roots of the trees become exposed. So we get the chance to see what the root structure should look like in a more 3D view

You can clearly see the roots divide and sub divide as they disappear down into the soil. It is clear there is real strength here holding the tree upright and with a little imagination then the roots could be fingers and knuckles.  Some fuse together as they cross and create ever more interesting shapes. We should not be afraid of this in our trees as long as the roots get smaller at further distances from the trunk then they will almost always appear natural.

Beech root divisionOne final image shows that to be convincing the stem need to flare before reaching the soil and the division begins well above ground.

To recreate this we need to ensure that there is a balance of growth around the roots and not allow a single root to overdevelop in exactly the same way that we would prune back an overly strong shoot above ground. Some people like to see all roots evenly sized but this is taking an unnatural step as the roots and branches never develop evenly – the top photo is perfect proof of this. The roots should spread and radiate from the trunk so do try to position roots when repotting. If the tree is presenting an image where it has been exposed to the elements the always try to show a little root on the surface of the soil as the weather will certainly have been eroding the soil, but a mature spreading parkland tree should really keep the roots hidden as over time the soil level will rise upwards through deposition of organic matter over centuries, following this tip will keep the image consistent and convincing.

Considering all of the above take a look at this bonsai and decide for yourself which side of the trunk looks most natural:

Root bonsai

Very Large Mtn. Hemlock Clump-

I am glad so many people are coming round to Hemlocks, and seeing these fantastic results it is easy to see the advantages of the species. Well done

Michael Hagedorn

This is one of those trees I’ve had in my yard a long time, and never done a follow-up post about. For one thing, it’s so large it’s hard to photograph. For another, I just didn’t get around to it.

All of the trunks come from one base; it’s one tree. The snows are so heavy where it came from that the young branches were brought down, and those branches later grew upwards and are now the trunks that create the clump.

This was the tree that started all my madness around finding new solutions for the slab question. Ironically, it’s the last tree I’ve put on a slab. This hemlock sat on a plywood slab for years, with me just dreaming about it, while completing other slab experiments. So, it benefited from other tree’s mistakes. Or my mistakes with them, I should say. Finally in 2014 it went onto…

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Deciding to remove a literati pine branch

Pine beforeI was recently tidying up a Scots Pine literati that I have a great fondness for and have been working on for many years on and off. The trunk has some lovely bark on the lower section and just enough movement to make it of interest. When I was given this tree it had already grown a little tall and leggy and would never be any good as a normal informal upright – the height suggested literati. The image on the left is how the tree looked after tidying up the old needles and a little light wiring to keep the shape of the pads.

Pine potential

To make this work the foliage has to be very light and after a very long hard look at this tree I wanted to see what it might be like without the lower branch. This seemed to be an anchor

to what should be a tall elegant tree reaching up for the heavens. Rather than commit it is always sensible to try to understand what the tree would look like without the branch. A white cloth against the white background gives an impression:

Pine after removal

The remaining pads have a consistency to them, the apex needing a little more development but clearly having the dome in the right place to link the other three. This gave me enoughconfidence that my initial hunch was correct and so the branch was removed. However it was kept on as a jin to suggest age and to point to the empty space emphasizing the floating feeling of the retained foliage.


One feature of note during this process of bark stripping was on one of the small branch stubs where the wire had clearly been bitten in the bark over the last year of growth, however when stripping the underlying wood as part of the jin it was revealed that the wood had not been effected. The soft tissue damage had not translated to the wood. When you think about it the wire can never actual cut into the wood itself but it is the growth around the wire which causes it to appear to bite in. If this is left for more than one growth season the new layer of cells added annually to the wood will eventually not have enough room and so the wire will affect the underlying wood. It is therefore perfectly possible that once the wire is removed the growth of the bark in the following year will start to normalise and the wire marks would slowly grow out. This is why wire marks are not as serious as they appear on thick barked species.


Styling a Windswept Larch

In a previous essay I made reference to an unconvincing windswept tree. Several people have asked if I could provide some more information about what a convincing windswept Bonsai would actually look like, so to help visualize. I have recently worked on a Larch with this question in mind. Instead of making a half-hearted attempt and failing to provide the answer I decided to go the whole way and reproduce something akin to a hawthorn I photographed on top of Dartmoor.IMG_9279

For those who don’t know Dartmoor it is where the winds first hit land after crossing the Atlantic Ocean – so pretty windy. Here’s the tree:

Notable features here include:

  • Very few verticals even the main stem despite obvious attempts by new shoots to grow upwards
  • Long extended horizontal branches
  • Every live branch tip is pointing to the leeward side as tips the other side get battered by the wind
  • The foliage only really survives where it is sheltered by other smaller twigs above it, creating a modicum of shelter
  • Overall an incredibly dynamic, but consistent image

For this demonstration I picked a Larch that already suggested a leaning image, due to the angle of its roots


This was a healthy tree recently collected with a good fibrous root system so I feel confident giving it a fairly dramatic styling at this stage.

The first step was a simple removal of any dead or damaged shots to clean up the tree, this made no overall change to the tree and I now had a clean slate to work with.

I decided to pull the trunk further downwards closer to the horizontal, I experimented with a gentle bend but decided that this would not really be possible so opted instead for pulling the whole trunk and securing underneath the pot, effecting an invisible change but putting the tree well on the way.

I removed any branches that were now obviously out of line with the idea of the direction of the blowing wind, one major branch that many would have been afraid to lose but fundamentally wrong for this tree. I highlight the branch:

Then came the always time-consuming but enjoyable task of wiring every branch that was not growing in the desired direction – for such a fundamental image overhaul this was in fact every single twig. This also gave the opportunity to add little twists and direction changes in the smaller branches to give an increased impression of the tree loosing shoots and having to regrow. So we end up with this after the styling


The lower branches will need to strengthen and some more will need to be removed from the canopy once shoots develop in the spring. However having a longer thin branch shows that the tree is able to develop a branch in this spot sheltered by its own branches and I will be careful not to allow them to thicken too much and dominate the image.

I am also undecided about the tiny jins which, now I look at the photo, add nothing of value to the image, instead I will replace them in a year or two with a jin of one of the external branches and at that time I may also add a small shari to the windward side of the trunk.

I will then try to find a suitable pot… but that will be a story for another day


Styling a raw Hemlock

Why do you never see many Hemlock in bonsai articles? They are great trees, very hardy and forgiving, small needles with an ability to back bud when healthy, flexible branches and an interesting bark when mature. So what is not to like?

The answer can be seen in that any work on this tree is likely to finish looking a little… scruffy. There is no other word for it, the needles stick out everywhere and the tips of the branches all tend to sag needing a lot more work to produce a beautiful magazine ready image after a session.


Take a wild collected Hemlock (Tsuga heterophylla) like the one above. Planted with two trunks in one with the thought to try something a little different but perfect for demonstrating what I mean. One dominant trunk and a secondary sub-dominant that will become the ‘child’ being nurtured by the loving arms of the parent.

First step was to remove all the dead and damaged branches. There was a reasonable amount of that in the canopy of this because, being a wild tree that had been grazed by deer it is inevitable that many small tips have lost buds and died back. Also the crown is so dense that some of the interior branches have died through lack of light. Once completed there is not much change visually but a little more light through the crown.


The branches have a strong upward tendency that does not work for what I intend to be a more mature image, so the brnaches need to be puled down quite violently. The tree is young, healthy and flexible so with a deal of care it is possible. The first main branch comes down to a more horizontal position to start the styling:


At this stage it was useful to prune and style the small child tree as its position would have less options. Now the position of the main branch the whole composition was in place it was possible to find the correct level for the main foliage pad to be supplied by the small tree. I decided it should be slightly lower to reflect the trees inferior position, but roughly equal in spread from the trunk of the main tree


(below left) Front – Parent is clearly protecting the child with an overall crown that could easily be possessed by a single tree.

(below right) Right Side –the child is closer to the parent but less distinct but a much clear feel that the main tree is embracing the smaller one.


Obviously after such a harsh first style there is some leggy growth that you may wonder why I left it – the Hemlock, like so many other species needs buds at the end of twigs, if it has these it draws vitality through the twig and can flush with back buds, and can then be pruned back. If these straggly twigs are removed now the whole branch could wither. Much better to err on the side of caution in such matters

So in the final images the overall first impression when compared to the result of a session on a nice tidy well behaved pine is… scruffy. But you need to be patient with Hemlock to get the rewards, once the trees throw a cloud of buds and the outlines of the pads thicken you will be pleased I promise.

Watering an evergreen bonsai – wartering blog part 2

Now for evergreen trees the myth of a growing season is even more dangerous as they do not give such clear clues as deciduous trees do when the buds burst in spring or drop their leaves in winter. Also it is possible that they come out of ‘hibernation’ and grow in the depths of winter if the days are warm enough (or if we stick them in a warm greenhouse).

The phenomenon that causes a tree to start growing is known as ‘day degrees’. It is simply the temperature each hour of the day added together to get a total figure for the day. When this figure is high enough the tree will start growing. So a hot day in winter can trigger a higher day degree figure than a longer colder day in spring when you might expect a tree to be growing. Whenever a tree is growing it needs water, so you must always be alert with evergreen trees that the soil remains moist through the winter. I also think it is worth repeating a sentence from the last blog: it is always prudent to ensure the soil is slightly moist as a desiccated soil can draw moisture reserves out of roots and could lead to ‘freeze drying’ (the same way food in the deep freeze can dry out if the packet is open).

Evergreen are also more able to be active at lower temperatures because they quickly incorporate water with their resinous sap, a substance able to withstand freezing at normal temperatures. The plant can pump this sap around the system causing growth to occur even at incredibly low temperatures. For evidence of this look at the growth rings of a felled tree – you will see wide summer rings where growth is at its most vigorous but material is added to stem diameter throughout the winter period.

Therefore it is safe to assume that the Growing Season never really stops regardless of the species and winter watering is needed. Now having said all of that of course trees are clearly more active in the spring and summer and need much greater volumes of water during hotter months.