Pruning your bonsai is an important part of creating a well-balanced bonsai and
ensuring your tree's health. The pruning style will depend on the style
of bonsai and type of tree you are growing. In general, heavy pruning
should be done when the tree is dormant. Light pruning can be done year
around. As you prune your tree, be sure to look at it from many angles
to ensure the tree is balanced.
Remove any branches that clutter the style you have chosen for your tree. In a semi-cascading style tree, for example, remove branches on the side of the tree that doesn't sweep outward. Prune the branches using a pair of bonsai pruners or a very sharp pair of scissors. Cut the branch very close to the trunk, but leave a tiny bit of the branch protruding from the tree to avoid damaging the nutrient delivery systems of the trunk and bark.
Prune to redirect growth. In the example of a semi-cascade style tree, pruning all the branches from one side of the tree redirects the tree's resources to the cascading side.
Prune any branches that cross and that are not conducive to wiring. You will likely encounter this when doing your initial pruning on a newly planted tree.
Prune any branches that point toward the front of the pot. Although this is a good general rule, there are some styles of trees where front pointing branches may be appropriate. In general, however, front pointing branches don't add to the balance of the tree.
Throughout the growing season, do light pruning on your tree's foliage. To limit leaf spread, clip the new growth on broad leaf trees back to the first two leaves growing from the branch. For junipers, pinch or cut off the tips of new shoots to prevent growth in that direction. Pinch back the "candles," or the center part with the growth bud, on pines.
Trim the leaves on deciduous trees that don't produce fruit or flowers. On branches that are weak, cut the tips of the leaves off about half way down the leaf. On strong, well developed branches, cut the entire leaf off. Leaf trimming should be done in the early summer. After a few weeks, the leaves should drop off and new, smaller leaves should grow back in place of the original leaves. Remove between 60 and 90 percent of the leaves, but be sure to leave enough green to allow the tree to produce energy for growth. If you are unsure of how many to remove, it is best to err on the side of a conservative leaf trimming rather than risk the health of the tree.