Pruning is essential for bonsai cultivation. Some of the most common techniques include clip and grow, pinching, and partial defoliation. Let us briefly go through each technique individually.
Clip and Grow
This is a simple technique that can produce tremendous results for deciduous trees and broadleaf evergreens in only a couple years. Essentially this technique minimizes the use of wire for shaping trees and rather utilizes directional pruning and cutting to the shortest internode.
First let us establish terminology.
The circled areas below are called nodes. At each node there is a dormant axillary bud in the visible crotch where the petiole and stem connect. This axillary bud contains an apical meristem which remains latent until growth is stimulated. The area in between two nodes is called the internode. No growth will emerge from the internode, so keep that in mind when pruning.
Below is a photo of the dormant axillary bud at the node. These buds are not always visible, but they are always present.
When we implement the clip and grow technique, we will prune back to one or two nodes. Over time this will lead to the development of many nodes in a tight proximity. Since each node has axillary buds this will make developing your bonsai much easier and aesthetically pleasing.
When pruning back to a node make sure the internode length is short and that the axillary bud is pointing in the right direction. If the internode is too long cut back to a tighter node. Long nodes are inefficient and aesthetically displeasing. Below I will show an example of cutting back to two nodes. Notice how the internode is compact.
If you continue this process, you will get very natural branching that wiring can not replicate.
Below is an example of the implementation of the clip and grow pruning method over the course of several growing seasons. The red lines show where pruning was done.
Now here is a warning, you must be mindful of the tree’s health with this technique. Every time you cut the tree you are depleting energy reserves and strength. If the tree is healthy this is no problem and it will bounce back quite quickly, but if the tree is weak it may dieback or not bud from axillary buds at all. So please be wary and considerate of your tree’s health.
This is one of the simplest and yet most powerful techniques we have at our disposal. Before I show the technique, we will first need to cover some important terms: apical dominance and auxin.
Apical dominance is the natural growth habitat of many plants that favors strength towards the top of the plant rather than the lateral shoots. In the natural environment this allows trees to compete for light and leads to the tree’s natural form. Note there is much variability in the growth habits and shapes of trees, but generally the tops of the trees are stronger.
Auxin is a plant hormone that contributes greatly to apical dominance. It especially gathers at shoot tips and is responsible for the “suppression of axillary bud development” (Hopkins & Huner, 2009, p. 313). The reason why this hormone is so valuable, is it gives you the ability to manipulate the growth habit of your plant. If you remove the tip of a shoot, you are essentially removing a concentrated amount of the hormone auxin. This will often stimulate back budding which is essentially the awakening of dormant axillary buds from nodes farther down a branch. We utilize this hormone by stopping the elongation of branches and redirecting energy to other shoots. Shoots that are pinched will lose their apical dominance and the shoots that are not pinched will exhibit more growth and vigor. This allows us to weaken or slow strong areas of the tree and redirect that energy to weaker branches.
Below I am showing the shoot tip where the apical meristem and auxin are located.
Next in the photo below I will simply remove the shoot tip. Now the auxin is removed which should cause back budding on nodes farther down the shoot. Removing the tip will also temporarily stop this branches elongation.
Partial defoliation & energy balance
Partial defoliation is another useful technique that accomplishes multiple functions simultaneously. The procedure is basic, leaves are simply cut off. This is done to let light into the interior branches/buds, reduce leaf size and to weaken branches that are becoming too strong. When trees are allowed to grow freely, they will often choose certain branches as their “favorites”. These favorites if left untamed will become branch leaders which eventually turn into the tree’s apex. Simply by removing more leaves on these stronger branches and leaving more leaves on weaker branches we can alleviate this issue and rebalance the tree’s strength.
Partial defoliation of larger leaves is also done so light can hit branches/buds in the tree’s interior. This promotes the health of interior growth because without sunlight, shaded areas will weaken and die.
Lastly, when large spring leaves are pruned off, the second flush of leaves is usually much smaller so this can additionally help aesthetically enhance the tree by reducing leaf size.