The reason for pruning will determine the limbs and branches to be removed from a tree or shrub. If the objective is to remove diseased portions, the cut should be made through healthy wood between the trunk or crowns and the infected part (Figure 11-9). The cut should never be made through the diseased wood or very close to it. This contaminates the pruning tool, which may transmit the pathogen to healthy parts pruned later.
If the objective is to improve the overall health and appearance of the plant, branches growing into the center of the plant should be removed. Limbs and twigs that grow across other branches can crowd the plant and cause sites of infection to form by rubbing abrasions through the bark. If more than one limb originates at a tree crotch, the strongest should be left and the others removed (Figure 11-10). Major structural limbs and twigs must be left so that no holes appear in the plant. Often overlooked is the fact that many secondary branches can stem from one older branch. The removal of one branch from a young tree can result in an older tree missing an entire side.
If the purpose of the pruning is to create denser foliage, as with evergreens, the center shoot is shortened or removed. This encourages the lateral buds to grow and create two shoots where there had been only one (Figure 11-11).
figure 11-10. Selecting branches to be pruned (Delmar/Cengage Learning)
figure 11-11. Evergreens are pruned in the spring if denser foliage is desired. (Delmar/Cengage Learning)