They leave it way too late!
A quality, healthy bonsai needs regular pruning to create compact pads of foliage, and to assist in reducing leaf size.
Most trees such as figs etc. If left to grow un-attended, will produce long leggy branches that will have an increase in distance between the pairs of leaves the longer they are allowed to grow.
As these branches grow (vigorously at first) they will also be producing vigorous root growth as they search for nutrients to feed this vigorous top growth, over time this causes the bonsai to become pot bound.
The vigorous root growth compacts the soil in the pot, and this makes it more difficult for the tree to get nutrients and water, which then causes it to begin to get sick, it will then start to drop any old leaves from the branches (the ones closest to the trunk!) leaving only the large leaves at the tips of long leggy branches!
This alone makes it very difficult to get a tree back to being a bonsai!
Best Pruning Practices
The best pruning practice is regular attention; major pruning can be done at the time of re potting and in the middle of the growing season if necessary, but compact healthy foliage and fine ramification of branches is achieved by regular consistent attention.
If you are following one of the 5 basic styles of Japanese bonsai, then your tree should resemble a triangular shape (scalene triangle).
For very basic pruning your branches or foliage that have grown outside of this shape can be the first areas to prune back, to reveal the outline of a triangle again.
Remove any un-wanted growth from above or below a branch, and rub off, or pinch any growth out appearing at the base of the trunk, or on old wood where a branch is not wanted.
Pinching back Junipers
The best way to keep a juniper in shape and to create clouds of foliage is to pinch the tips of the new growth out by using your thumb and forefinger and twisting.
This removes the growing tip from inside the needles, without causing browning or die back that can occur if cut back with scissors.
Keep juniper growth thinned out to avoid pests hiding among the fine needles.
Alternate or leaf Pairs
To improve branch ramification on trees that grow pairs of leaves or alternate leaves along a branch, can be done by cutting lateral growth back to a pair of leaves, or to a single leaf pointing in the direction of the next shoot you want to grow.
Bonsai pruning Secrets
You don’t have to be a bonsai master to keep a tree healthy and looking good, it just takes a little bit of regular attention.
As you learn more about how to bonsai you will feel more confident in the amount of pruning you do.
The secret is not to leave it till it is stressed and over grown before you do something about it, as this is when it is more likely you will kill a tree, or have a large amount of die back leaving a tree that no longer resembles a bonsai and will take years to, or never recover.