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


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