A tree usually requires one heavy pruning in its life to establish its basic form. After this initial pruning, shaping is done by nipping. Nipping, or pinching back, is done to shape and develop the trunk and to control the overall size of the plant. Nipping controls new growth before it becomes so dense that it must be pruned.
A twiggy plant can be made more dense when it is nipped. When all terminal buds on a branch have been pinched, several side shoots develop. In this way growth is stimulated. This will give the plant a bushier appearance.
Nipping is done not only to shape a plant but also to develop more luxuriant foliage. As the new growth tips show up, nip them with your fingers, twisting rather than pulling. Also nip off tiny spurs that appear on the trunk or along heavy branches. These may develop into unsightly suckers that will leave scars when removed. Do not overdo this removal; be careful not to damage the foliage you leave on the plant.
After the top of a bonsai is pruned, trim the roots. Try to keep all fibrous roots and maintain a balance, if possible, of one branch for one root. Remove any roots that were damaged in digging. Leave the surface root system intact and make it appear as if the roots cling to the soil surface. Prune roots with sharp, sloping cuts to avoid damaging them.