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Needle plucking is an essential tool for pine bonsai maintenance. It allows air and light to penetrate the outer foliage to increase the health and vigour of inner shoots and branches. It also helps to spread energy throughout the tree in the same way that bud selection and candle pinching do.
Combined with pruning of the current years growth on a Pine bonsai, needle-plucking is also the best way of prompting backbudding as well as controlling the size of a pine bonsai.
Timing is important; it should be carried out after the new growth of the current growing-season has extended, from mid-July (late-Summer) until Autumn.
Both old and new needles are plucked according to their position on the tree. The basic principal behind needle plucking is that the more foliage or needles a branch has, the more vigorous it is; by reducing the amount of needles on a vigorous area of the tree (such as the apex) in comparison to the number of needles a weak area has, vigour is distributed more evenly.
As a basic rule leave less needle-pairs on the upper shoots and more on the weaker, lower and inner shoots. Often no needles are plucked from inner shoots to preserve their vigour. The actual numbers of needles that are removed will depend on the needs and strength of the tree. With a very vigorous tree it may be possible to leave as little as 4 pairs of needles on the upper branches, 6 or 7 pairs on the mid-level branches and 8-12 on the lower branches. Base your starting number on the lowest, weakest shoots since you can only decrease strength with this technique and not increase it. Do not remove so many needles that the overall vigour of the tree or branch is lost.
Trimming and Forcing Back-Budding
To force a Pine to back-bud is ordinarily difficult . However, shoot trimming is a useful technique for trying to force back budding and generally increasing the number of buds on a tree.
In late Summer, the current years' growth is pruned. New shoots are pruned according to the desired length of the enthusiast; where a longer branch or shoot is required the new shoot might even be left unpruned. Where ramification (or density of buds) or containment of the size of a branch is required, the new shoot might be pruned right back leaving just 2 or 3 sets of new needles.
It is at this point, where needles are left at the tip of the newly pruned growth, that the shoot will produce new buds through the Winter and following Spring. It can also cause the tree to produce buds further back along the branch, where old needles have been recently plucked or sometimes even on old wood.
Note: The health and vigour of an individual Pine bonsai varies from tree to tree and the ability of a Pine bonsai to withstand bonsai pruning techniques varies from species to species. Weak trees and weaker species (such as Japanese White Pine) should not be pruned as hard as healthy, vigorous species such as Japanese Black Pines and Scots Pines.
I collected this Scots Pine/Pinus sylvestris, a 2-needled pine native to Europe, 5 years previous to this image being taken and had been 'chasing' back the foliage to reduce the length of the branches and bring the foliage mass closer to the trunk ever since.
This required me to allow the new candles to extend freely into new shoots (encouraging health and vigour in the tree) before then pruning the foliage mass hard each late Summer (August in the UK) to prompt backbudding closer to the trunk.
In the image above, the Scots Pine is seen in early August prior to needle plucking and shoot-pruning; each branch has a dense mass of needles growing from its tip.
To correctly prune and pluck, the tree is methodically worked over, branch-by-branch.
The older, darker needles on this branch grew last year. At their tip, two new buds emerged in the Spring and have resulted in two new shoots covered in the lighter green current-years needles (grasped between my thumb and fingers).
Further back along the branch (at the top of the image), an adventitious bud has also emerged in the Spring and extended new needles, although it is much smaller and therefore weaker.
The same branch after needle-plucking. The previous years needles have been removed, these can be plucked by hand or as I have done in this case, simply cut away, leaving a small stub behind. These stubs are now potential sites for new buds and shoots to emerge next Spring.
Note that it is safer not to prune back the entire branch to the newly emerged adventitious growth until it becomes stronger, in future years.
This branch has had its older needles plucked. It could now have half of the new, current years needles plucked as well.
However......buds will appear on the tips of these shoots next Spring and this amount of shoot extension is not required on this branch........
.......And so the shoots are pruned back. The new buds next Spring will now appear closer to the branch. It is now not necessary to reduce the number of (new) needles.
This very strong, apical branch has a great number of new shoots (and needles) emerging from its tip and it needs pruning to balance it with weaker lower branches as well as ensuring that no branch divides into more than 2 sub-branches.
The same branch after removal of all shoots that were surplus to requirements