20 THE COMPLETE GARDEN 



branches will not interfere with pedestrians or vehicles. The roots of 

 street trees are more confined than those of other trees and they re- 

 quire top pruning to balance with the root system. Pruning should 

 aim to preserve the natural habit of the trees; but they should also 

 be kept symmetrical in form. If the tops become too thick and ex- 

 clude too much hght they should be thinned out. Main laterals, 

 however, must not be disturbed, but rather the shoots that spring 

 from these main laterals should be removed. 



Specimen trees on lawns require little pruning except to prevent 

 bad crotches (which if left might cause splitting), to shorten branches 

 which may affect the symmetry of the tree, to remove dead wood, and 

 sometimes to remove (as in the case of maples and pin oaks) some of the 

 finer interior branches in order to give more "character" to the tree. 



It is generally best to do the heavy cutting in winter, while the trees 

 are dormant. Pruning in early spring or summer may cause the 

 tree to "bleed," with a consequent check to the root system from the 

 loss of food. This is especially true of maples. One advantage, how- 

 ever, of spring or summer trimming is that the tree will recover more 

 quickly and start to heal the wound, which would be impossible during 

 the winter season. If trees are pruned in winter the " shaping up " and 

 removal of small pieces of dead wood should be done after the leaves 

 appear at which time symmetry can be better judged and all dead 

 branches can be more easily discovered. To assure the least possible 

 injury from exposure to climatic conditions winter pruning, if neces- 

 sary, should be delayed until the danger from the more severe winter 

 conditions is past. 



Broken and diseased limbs must always be removed, and secondary 

 growth and suckers cut, to open the centre of the tree to the sun and 

 air. When limbs are pruned they should be cut back to a bud that will 

 grow outward. 



When larger branches are entirely removed, the cut should 

 be made at the base of the branch and parallel to the tree trunk. 

 No stump at all should be left, and care should first be taken to under- 

 cut amply on all heavy Hmbs so that when the cut on the upper side is 

 completed the branch will not split the bark from the trunk. All 

 other cuts, such as removing portions of branches, should be made 

 perpendicular to the axis of the branch which is being shortened. The 

 cut should always be clean, with no ragged edges left (See Plate V). 



Never cut back the leader on trees that are excurrent, such as oaks, 



