White pine bonsai pruning
Why does a White pine bonsai need to be pruned ?
The pruning of a Japanese white pine bonsai mainly serves to control the growth vigor and is the most important technique of bonsai design in addition to the wiring. Without pruning, the quality of the bonsai quickly deteriorates. This must be taken into account when caring for bonsai.
A White pine (Pinus parviflora or Pinus pentaphylla) grows mainly on the outside of the crown. Inner and especially lower areas of the bonsai tree crown grow weaker (due to lack of light) and usually die sooner or later.
This is a perfectly normal process for a White pine in nature. The tree wants to grow up, grow up quickly so as not to be shaded by the undergrowth or other trees. If this happens the sun is missing for growth. And if the light is missing, less photosynthesis is done. The tree grows more slowly and the problem (shading by other trees) keeps getting bigger. At some point the White pine dies in the shade.
To prevent this from happening, the White pine must quickly grow upwards. To make this possible, the White pine, like most trees, puts all of its energy into the growth of the upper areas of the crown. At the same time, the growth of the lower areas and the shoots inside the crown is neglected.
This different growth vigor is controlled by plant hormones. The plant hormones are mainly formed in the shoots and transported downwards in the stem. There the hormones inhibit the budding of further buds. The tree does not want to put any energy in shoots that get too little light from its own crown or other plants.
This suppression of branches in the lower area is called apical dominance, i.e. the apex (= the tip) dominates (= controls) everything that is below it. All pines trees are strongly "apical dominant".
Apical dominance, which is good for survival for the pine trees in the forest, can become a problem for our trees. Here we want a dense and finely branched crown. The lower areas should not slowly becomes weaker. We need them (mostly) for a balanced design.
In order to obtain a finely and densely branched crown, it is very important in a bonsai tree to control the normal growth. We have to break (or suppress) the apical dominance and direct the growth vigor to the areas that are important for styling. If we succeed then the bonsai tree will develop as we want it.
Before pruning
Before cutting a White pine, you should think about the future shape. The White pine bonsai shown here has a light and irregular crown. In order to make it denser and more uniform, we have to cut off in the long term everything that grows outside the red line.
How to prune ?
Above all, when cutting a White pine bonsai, it is important to control the growth of the bonsai. That means we have to weaken the growing areas of the crown (top and outside) so that the lower and inner areas get more light and do not die off
Before pruning
Such a pruning of a Japanese white pine bonsai can often only be done in steps over several years.
Why prune in partial steps ?
With many deciduous trees, if desired, the crown can be cut back extremely radically in one step (e.g. Satsuki azalea or Chinese elm). Usually the deciduous trees then create a lot of new buds and often have a finely branched crown after a few months.
That doesn't work with White pines bonsai trees. If all needles and buds are cut off at the end of a shoot, this shoot will most likely die. That is the reason why we have to proceed slowly and gradually.
First, the strong shoots or the strong areas are selected. These can and must be cut back more. The weak areas are often not cut at all in the first step. Only when they have become stronger over time can they also be pruned so that they become denser and form beautiful needle cushions.
When cutting back the strong shoots (areas), there are several ways to reduce them:
- 1. Remove strong buds at the end of winter
- 2. Shortening stronger candles shoots after budding
- 3. Complete removal of individual young candles
- 4. Partial shortening of older branch parts
- 5. Shorten or remove needles
Removing strong buds
At the end of winter, the new buds can be clearly seen on the tips of the shoots of pine trees. Usually there are several buds that grow close together. The center bud is then usually much thicker than the buds around it. This bud can be easily broken out with your finger. If the shoot is to be weakened further, further buds can be broken out. The strongest buds are always removed first.
Shortening stronger young candles after budding
The remaining buds then sprout in spring and, depending on the type of pine and growth vigor, grow quickly. These young candles can be easily broken off with your fingers shortly after they have sprouted. A few weeks later, you need a bonsai scissors to shorten the candles.
Here too, the same pattern is followed: what is strong is shortened more strongly, weak candles are hardly shortened or remain untouched in weaker areas.
Complete removal of individual young shoots
Once the candles have unfolded, you can further shorten or even remove the stronger young shoots. It is often good to let 2-3 pairs of needles stand and only remove them when new buds have formed inside the branch.
In very strong areas of the White pine crown, the entire new shoot sometimes has to be removed (red line in picture 3, both candles are removed).
Partial shortening of older branch parts
If the removal of entire young shoots is not enough to slow down the growth of the strong branches, then a whole part of the branch can also be cut off. But always keep in mind: branches without good needles end up dying. That means if a branch is to be kept in the long term, a few good tufts of needles must still remain at the end.
Shorten or remove needles
As can be seen in picture 5, a rapidly growing area can also be weakened by cutting the needles.
After partially or completely cutting off the pine candles, the candle stumps often bleed heavily. After 1 minute, a clearly visible drop of resin has formede. With 1 candle - no problem. If hundreds of candles are cut from large pines, this can cost the tree a lot of strength. A cut back in partial steps over 2-3 months would then be better.