Regular pruning is one of the core practices of bonsai, and in many ways, allows practitioners to express their individual style.
There are few primary ways that bonsai-ists maintain their trees. The first method is maintenance pruning to maintain the plants desired shape. The second is structural pruning. Structural pruning is more intensive and geared toward the overall structure of the plant.
Before diving into pruning, a quick note on tree growth. Typically, trees grow more robustly toward the top. This natural distribution of growth at the top of the plant is called ‘apical dominance’. For a tree, this is the mechanism that allows it to grow taller, and avoid being out-shaded by competitors. What eventually ends up happening, is that the lower branches die, while the upper reaches grow out of proportion to the rest of the plant. Unfortunately, this pattern is not necessarily desirable for bonsai. Pruning counteracts this.
Back to pruning.
Maintenance pruning is simply an exercise in trimming away branches or shoots that have outgrown the canopy shape the grower is after. For deciduous or tropical trees, this can be done with pruning shears. In coniferous trees, it is better to do this by hand. This type of pruning can also be done by “pinching” off buds that are growing in an undesirable direction.
Structural pruning is more intensive. It involves trimming larger more mature branches. Here it may make sense to consult a styling guide, as once these branches are clipped, there is no going back. Having said that, this is the step where you truly decide how the bonsai will look (no pressure). Symmetrical, asymmetrical, short, stout, long, lean? It’s entirely up to you.