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


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.

P1000504 P1000505 P1000506

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

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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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


Collecting Trip New Years Eve 2013

Collecting trip for Wild Bonsai – New Years Eve 2013

Before reading anymore it is strongly recommended that everyone reads an excellent article by Walter Pall on the theory and ethics of collecting trees from the wild at:

The article focuses on collecting trees from the most inhospitable climates of the mountains. As we just don’t have the same quality of mountain as those Europeans it is quite possible for the enthusiast to find really good quality material much closer to home. Indeed this collecting trip was no more than 15 minutes from home! The key feature for me in looking for wild material is a combination of 3 factors – mature seed trees of the desired species, grazing and permission from the landowner.

Without the first of these there is just no point in combing the area as you will never find anything. Certain tree seeds can travel miles on the air but these generally do not produce high quality bonsai (Ash, Birch).  Without the second the tree seedlings will race upwards producing tall thin whippy stems racing up for the light against all the competition, so a ‘normal’ woodland setting provides thousands of young trees but the search for good bonsai yamadori is usually fruitless.

So on New Year’s Eve 2013 I set out to a spot I have identified whilst walking the hills over the summer as being of good potential. There area in focus is about an acre of open ground surrounded by stands of tree species regularly seen as bonsai (Larch, Scots Pine, Beech and Western Hemlock), all throwing their seed. The area is occupied over the summer months by cattle, this acts to trample taller trees snapping out any potentially leggy trees, they also graze the tender young shoots giving a pruning far more regular than most bonsai enthusiasts can manage!

Collecting trip landscape

I was not disappointed with the find of many trampled chewed sorry looking specimens, who at this particular visit were also sat in deep puddles after all the recent rain. Many of the trees were decidedly not healthy, being sick and yellow, these were all left to their fate out in the wild. However some were a lush green despite the treatment, these got a closer look as they would have the strength to withstand uprooting

.Collecting trip 2

The first find was a Western Hemlock about 60cm tall, a quick investigation revealed a good root structure, and great nebari and taper. When testing with the spade it was clear that the roots were spread horizontally over a stony layer of soil about 10cm deep. This was a great bit of luck as it exactly what we would try to achieve in bonsai with the wide spreading roots in a relatively shallow pot. There was a good fibrous root system close to the trunk and not many thick roots.

The tree was bundled up securely to keep a good quantity of forest soil. This serves 2 purposes, the first is that keeping this soil intact after severing so many roots will give the tree the greatest chances. Secondly the soil is perfect for this tree to grow in (any doubts check out the 30m tall specimens not that far away, it will also contain mychorrhyzal fungal associations that will act as additional roots for the tree. A lot has been said about these beneficial fungi but many people assume that there is only one type and that all they need to do is give a tree a dose of spores and then sit back – job done. Few realise that there are thousands of different strains of fungi, some that would be perfect with one tree will be totally incompatible with another species, therefore the only way to be certain is to take some soil from the wild and mix in with the new soil

On returning home it was potted up in a generously sized pot to allow the roots as much room as possible to recover. In order to balance the reduction on root I also pruned the branches to maintain the correct root branch ratio and take some stress off the roots. This also begins the development of the tree’s structure and you can see the informal upright shape and the taper in these before and after photos. The final photo was taken 6 months later after a second prune and well ready for a final prune of the year to get it ready for the winter – clearly a healthy tree!

Collecting trip WH

2014nov 004

Windswept trees as a bonsai image

At Raw Bonsai we are focused on taking our inspiration from nature and suggest that a truly convincing image can only be created in Bonsai if you understand the natural processes involved in shaping a wild tree.
Featured image

Let’s take a few moments to think about a convincing windswept image. I will start by introducing a windswept beech at the recent Bristol club show. Now fundamentally this is a lovely tree with a lot to recommend it, graceful movement in the trunk with a nice unusual shari, good root formation and well developed branching, not to mention a really good pot that brings out the silver in the bark:

So what is wrong with it?

The natural reaction to a tree growing in strong wind is for the buds in more sheltered locations to develop at the expense of those getting battered on the windward side of a tree. Any location will have a prevailing wind and the tree will lean away from this direction due to the cold dessicating effect of the wind, possibly even some salt laden spray in close to the coast. It is this and not the power of the wind that causes a windswept tree, unless it has simply an abnormal gust blowing an established tree over, but that is something quite different. So a bud in shelter will develop in a normal way, but instead of growing upwards any part of the bud tempted to do this will raise its head above the parapet and get buffeted by the wind, so instead it will grow into calmer air on the windward side fo the tree. Of course a slight steady upward growth will be possible but think of the correct growth like a staircase one step up and one step along.

The next image is a photo of a beautiful old hawthorn on the top of Dartmoor.IMG_9279

The whole image has a single direction of flow and the top is virtually flat as the wind sheers off new shoots. Of particular note is the lower branch, a young off shoot that has been able to develop quicker and therefore thicken up more than the older true trunk above it.

Take a moment now to compare it with the Bonsai image above and it becomes clear to me that a few of the branches to the right of the canopy really need to be removed to keep the flow in line with the angle started in the trunk, to do anything else is unnatural and unconvincing.

The problem for me is that the angle of the trunk suggests a very strong wind pressure throughout the life of the tree if it had grown in the top of a hill. A wind strong enough to create the dramatic lean would carry through to the finer twigs.

The same theory applies in a less windy place – consistency of the prevailing wind needs to be considered. This beech is set just under the brow of the hill and so the lower trunk is not in a location totally inhospitable but as the crown gets higher up it does get into the wind and the effects become more noticeable