Bonsai being living growing plants need from time to time be pruned to maintain their shape and more importantly their health and vitality. Pruning a Bonsai shoots, lets in light, air which helps strengthen and fortify the remaining leaves and branches and also encourages new growth; which in turn adds new and fresh sources of nourishment for the tree.
Essentially for the development of a Bonsai there are two primary approaches to pruning which have are motivated primarily by two distinct goals of Bonsai development. Structural Pruning is invariable driven by an artistic need to shape and coax the tree in to a new form, while Maintenance has primary goal, is horticultural in nature and deal with enriching a plants growth and vitality, by encouraging new shoot development and ensuring the bonsai tree does not become to big for its pot. If maintenance pruning is carried out with care and timeliness; internode distances are decreased, branch ramification is increased, inner growth and branching is developed. All of which invariably leads to the bonsai looking more mature and improves the over all aesthetics of a bonsai tree, and hence a secondary goal of maintenance is artistic in nature.
Maintenance pruning is undertaken to maintain a Bonsai's size and shape and encourages new growth and tree development. Maintenance pruning is carried more or less around the year, but is perhaps most need when the tree is at it zenith of growth. This can help encourage the tree to continue growing, and further it's strength and development. If you have a Bonsai which produces flowers a particular time of year, it will also help to encourage more blossoms. Even non-flowering varieties, however, will require a certain level of maintenance pruning throughout the year. The heaviest pruning is perhaps carried out late spring through most of the summer. Often refinement pruning and minor structural pruning can also be carried out in late fall and the early parts of winter, in deciduous trees, as the plant begins to go dormant an you begin to see the fine branching of (or ramification) of the tree.
Shoots and Leaf Pruning
Shoot and Branch Pruning is one of the key shaping tasks in Bonsai Training. Without shoot pruning your Bonsai will quickly lose its shape no longer look like a Bonsai and will outgrow it pot rapidly.
Shoot and Leaf pruning can be carried out through out the growing season and is carried out when a lot of new growth appears and begins to unbalance the shape of the Bonsai.
Use a sharp pair of long handled scissor, and cut back twigs, that have grown about 5-6 pair/sets of leaf on them (fig A), to leave about 3 max 4 sets of leaf nodes (Fig B). In a few weeks you will find new shoots have grown at the leaf nodes (Fig C).
Pruning of Chinese Elm at the 2:20 min mark if you want to jump straight to it :)
Figures E,F and G show the same principle as applied to a Bonsai. In Figure E the Bonsai shows signs of extensive Shoot Development and it is beginning to lose it shape and compactness. Buy pruning the long run away shoots you begin to get back the basic shape and silhouette of the original bonsai. In a few weeks this further improved as new shoots and more branching begins to grow, increasing the finer branching in Bonsai while at the same time the leafs sizes are also much reduced. Making the Bonsai look much more proportionate and like a real tree.
While you are doing your pruning ensure that you remove all deadwood and ugly stumps from the tree, and covering all large bruises with cut paste to prevent excessive loss of sap from the tree.
It is also advisable to water the tree thoroughly once it has been pruned and to regularly spray the tree over the next week or so to help it recover quicker from the pruning.
Small Twig Pruning
Occasionally you need to thin out the crown of a Bonsai that has got to much of foliage and growth (Fig H) to allow more light and air to reach lower branches on the Bonsai our you could be in danger of losing them.
While thinning out the crown of the tree, you may require removing small branches, rather than just shoots. Mark out the Branches you want to remove with a marker pen or use piece of wire to identify them (Fig I). Mark out any Braches that you feel whose removal will not affect the over all structure of the tree, while still letting light to the lower branches.
Once you have identified the branches and twigs remove them with a pair of strong Japanese Style Bonsai Scissor or a Branch Cutters. Remove any dead wood and stubs left from last season using either a pair of Knob cutters. Branch Cutters and Knob cut cleanly leaving a concave shaped cut, which heals over into a flat surface quickly.
When using a Pair of Scissor cut across a diagonal of the Stem it is easier and offers a cleaner more natural cut. When using a Branch cutter align the Branch Cutter the length of the cut follows the flow of the sap up the branch, this way the wound heals faster and with a minimal scar.
When doing a thinning exercise you may also want to remove some of the older larger leafs from the steam, this lets more light into the crown encouraging new shoots and new growth which are now much smaller. You should end up with a tree that while it still maintains its' original and it now allow much more light into the lower branches and
Budding and Pinching
Conifers normally need De-budding and Pinching, which refers to the removal of the tips of the Growing Needles to encourage more branching and to create a more compact shape. You often need to pinch out whole needles, especially in spring when a lot of needles develop. Letting numerous amounts of needle grow unchecked puts an unnecessary burden on the Bonsai and will also result in its losing its shape.
In Pines, for example, often upto 6 new needle buds can sprout at the growing tips. Leave up to 3 needles that are growing in the desired direction and pinch out the strongest of the buds.
Leaf Pruning refers to the defoliation of a Bonsai Tree, which is carried out to encourage the growth of much smaller leafs. This is primarily on Deciduous trees just after the first flush of leafs has settled in (Fig P). All leafs from the tree are snipped away at the base of the leaf leaving the leaf petiole (leaf stalk) on the Branch (Fig Q).
The leaf petiole falls of and a soon a new flush of much smaller shoots and leaves follow (Fig R). This help with leaf size reduction and helps make for a more 'natural' looking tree,
This is an advanced technique and requires to be carried out at the right time of the year or the tree may not recover from it.
Structural Pruning is resorted to when the Bonsai need to undergo some radical or structural change to its shape and usually involves removing Primary Branches of a Bonsai. Structural Pruning is a more advanced technique as it can puts the tree under duress and need to be carried out with care and at the right time of the year, usually when the tree is dormant and only through 'controlled' amounts of heavy pruning. The amount that you can prune is dependent on the species, the time of the year and the environment in which the tree is allowed to recover. More or structural pruning will be covered in advanced Techniques section.