On the other hand, orientation of lateral branches at 45° to 60° angles from the vertical or main shoot reduces the vigor of shoot growth near the apex and increases the number and length of laterals along the limb further from the apex. On horizontal limbs, apical dominance is totally lost. Without apical dominance to control their growth, lateral buds on the upper side of horizontal limbs develop into vigorous, upright shoots, called water sprouts. As they develop, water sprouts show very strong apical dominance. Water sprouts are a common problem on the upper surface of flat limbs in fruit trees and are removed by pruning.
A Plant’s Response To Pruning
By removing the apex, pruning temporarily destroys apical dominance and stimulates the growth of lateral buds into shoots. Pruning also reduces the size of the above-ground portion of the plant in relation to the root system, so root system services a smaller number of shoots and buds. The relative uptake of water and nutrients by the remaining shoots and buds increases, and a flush of growth occurs. Generally, the more severe the pruning the greater the resulting growth. Pruning generally stimulates growth near the cut. Vigorous shoot growth will usually occur within 6 to 8 inches of the pruning cut. However, growth on limbs having a 45° to 60° angle from the vertical will develop farther away from the cut. Pruning can also stimulate growth by allowing more light to penetrate the canopy of the plant. Pruning a young plant will stimulate vigorous shoot growth and will delay the development of flowers and fruit. The length of the delay, of course, will depend on the species pruned and the severity of the pruning.
Types Of Pruning Cuts
Real Green Pest and LawnThere are two basic types of pruning cuts, heading and thinning. Heading removes the terminal portion of shoots or limbs. By removing apical dominance, heading stimulates growth near the cut. It also is the most invigorating type of pruning cut, resulting in thick compact growth and a loss of natural form, as in the case of a formally pruned hedge. Sometimes ornamental shrubs along a foundation overgrow their planting space and are rejuvenated by heading to within 12 inches of ground level. Thinning removes an entire shoot or limb to its point of origin from the main branch or lateral. Some shoot tips are left undistributed, so apical dominance is maintained. As a result, new growth occurs at the undisturbed shoot tips while lateral bud development and growth is suppressed. Thinning is generally the least invigorating type of pruning cut and provides a more natural growth form of plants. Important in maintenance pruning, thinning cuts are used to shorten limbs, to improve light penetration into plants and to direct the growth of shoots or limbs.
Drop-crotching, a form of thinning used to reduce the size of large trees, involves the removal of a main branch by cutting it back to a large, lateral branch. The cut through the main branch is made parallel to the angle of the remaining lateral. When removing large tree limbs, a series of three cuts are recommended in order to avoid tearing the bark along the main truck and severely wounding the tree. One undesirable form of thinning is the bench cut, where a vigorous upright limb is thinned to horizontal limb. Vigorous, upright shoot growth, called water sprouts, often result from the “bench” area because of the absence of apical dominance in the horizontal limb. The correct method is to make the thinning cuts to limbs that are similar in angle to the limb being removed but not more than 45° to 60° from vertical. Shoots or limbs having narrow-angled crotches are weaker than those having wide crotch angles. The bark of the adjoining branches becomes tightly compressed, preventing normal wood development. Winter ice, trapped down in crotches, often causes narrow-angled branches to split.