Defoliation

Defoliation is the practice of stripping some or all of the leaves from a healthy, vigorous deciduous bonsai during the growing season, which prompts the tree to push a new flush of growth. That new growth typically comes in with smaller leaves and shorter internodes, which improves the scale and density of the canopy on a tree that is otherwise developed but has oversized foliage.

This technique is only appropriate for strong, well-established deciduous trees with a healthy root system, since defoliation removes the tree's food-producing tissue and demands energy reserves to recover. Conifers and weak or recently repotted trees are generally not defoliated, since they lack the vigor to push a full new flush of growth without significant stress.

Partial defoliation, removing only some leaves rather than the whole canopy, is a gentler approach used on trees that are healthy but not at peak vigor. Defoliating a tree that is already stressed, sick or recently repotted is one of the more serious mistakes in bonsai care, since it can push a weak tree past the point of recovery.