We spend a lot of time twisting branches or cutting them off and then stuff the poor tree into a tiny pot, all in the name of creating something really cool. But think about what the tree wants to do. Let’s put ourselves in the position of the tree. It knows that somewhere down the road in the future it will be overcome by bugs, drought, rot or bad weather overloading it with snow. In short, it has a limited life even though it might be very long. The primary goal of the tree is to generate little trees that will perpetuate itself. It can only this through seeds. But seeds face a tough life. Many are eaten by birds or other animals and many of the rest do not land in a place where they can grow, like for instance in a river. Some seeds can survive and start to grow but the little tree is eaten by a deer or other animal the tree copes with the vanishingly small number of seeds that survive and grow into trees by making as many seeds as it can. It needs to do this by growing as big as it possibly can. So how does it do this?

A big tree needs a lot of wood to hold up the top of the tree. Wood is generated by the marvelous process of photosynthesis where water and carbon dioxide in the air are made by the action of sunlight into chemicals which are the building blocks of wood. The product of photosynthesis is frequently referred to as energy for the tree but it has nothing to do with energy. It is wood that is the sole fate of these products.

The key catalyst of this process is chlorophyl, a chemical which is green. All the green leaves that you see on any plant is due to the presence of chlorophyl. Chlorophyl is big molecule that is composed of 6.2 % nitrogen and 2.7% magnesium. We feed our trees with a nitrogen rich fertilizer which we hope can lead to ever more chlorophyl available to the tree but we usually don’t think about magnesium which is a necessary component of chlorophyl. Our trees grow splendidly without adding magnesium to our fertilizer. That is because it is present in tap water, clay or water that has spent time flowing over rocks. According to East Bay Municipal water, their analysis shows that tap water contains typically 1 to 15 ppm magnesium. The higher numbers come from water stored in clay lined reservoirs which suggests that clay is a source of magnesium Although we do not think of akadama, a component of many currently popular soil mixes, as a fertilizer it would appear that it is a source of magnesium. Also, both lava and pumice are potential sources of magnesium. Our soils mixtures can supply all of an essential element for a tree without our really knowing it.

The tree has a big problem. It wants to grow as big as possible but if all the buds on all the branches grow at the same time, the tree turns into a big ball of leaves which limits growth because most of the leaves in the ball do not see any sunlight so photosynthesis can’t take place. The tree knows that long branches expose all the leaves to sunlight so it can maximize the production of needed wood. It must be able to manage where growth takes place and it does this by making a chemical called auxin which is a growth hormone. It is mainly produced at the very tips of growing branches and from there it moves throughout the plant. Auxin does not promote growth as you might think but it inhibits growth. The little buds along the branch will not grow in the presence of auxin so the branch can grow very long so the presence of sunlight on the leaves can be maximized. If you want a bushy tree, you remove the source of auxin by pinching the ends of the branches. With the source of auxin gone, the little buds can now grow. Some trees produce more auxin than others which is why some trees are naturally bushier that others.

The tree knows that growing long branches requires an ever-thickening trunk to hold up increasing size of the canopy of the tree. Here is where auxin plays a different role. Auxin produced by the growing branch tips travel to the trunk and settle in the outer edge of the truck which is where trunk expansion takes place. Here the auxin promotes the growth of the edge and the trunk gets bigger. We often hear that planting a potential bonsai tree in the grown leads to a fatter trunk. What really happens is that when in the ground we let the tree grow and with many tips of branches all producing more auxin and this is what makes the trunk get fatter. When we pinch and prune our trees to make them into presentable bonsai, we remove the source of the auxin at the growing branch tips which allows the back buds to grow but carries an unintended consequence that the tree trunk does not grow fatter.

When we work on our trees, we frequently take them for granted. They usually do more or less what we want them to do which delights us. There is lot more going on that meets our eye. They are truly fascinating subjects if we get to know them.