Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
March is the major month for pruning tree fruits, grapes, and cane fruits. Pruning earlier than March often stimulates plants too early and can result in later cold damage; pruning after plants have leafed out can result in loss of plant vigor.
On young fruits, pruning is used to develop the plant architecture and to allow for good root systems to develop. On bearing fruits, pruning is used to maintain productivity. In commercial orchards, pruning is done to create maximum fruit bearing surface, to allow sunlight to enter, to allow air to circulate throughout the tree canopy, to promote good spray penetration, to renew fruiting wood, and to maintain growth or vigor in all parts of the tree. Pruning is also a way of regulating the fruit load on the tree in the current season and from season to season.
On bearing tree fruits, the first step is to remove any suckers from the base of the plant. The second step would be to remove damaged or diseased wood. Remove this back to a main branch or scaffold limb and make the pruning cut at the branch collar (do not flush cut). Next, remove any watersprouts. These are rapidly growing upright shoots that form along the trunk or scaffold branches. Depending on the training system, additional pruning or training will be needed to maintain proper plant shape or height. For example, in fruits trained to an open center, remove any inward growing material. For central leader systems, remove excess branches to the main trunk. Finally, thin out flowering wood or spurs as necessary to reduce fruit load and make pruning cuts to encourage future fruiting wood development (this step varies considerably depending on the type of fruit).
In bearing grapes (generally starting the third year after planting), pruning is used to set the fruiting area for the season and for renewing young canes for the next year. Cane pruning is the usual system for Vinifera types but is also appropriate for some hybrids and American types. In this system a permanent trunks is established (often two trunks are established) to the wire, and every year two canes arising from the trunk, each 8-10 buds long, are selected and tied to the wire (one each direction), and all other canes are cut out. Canes should be about the thickness of your little finger and should come out from the trunk as close to the wire as possible. These canes should have buds fairly close together (avoid large thick canes with buds spaced far apart). Another system, often used with hybrid grapes, is the cordon or spur pruning system. With this system, in the second season, one cane is trained to each side of the trunk, and they become permanent arms that remain as the base on which short spurs are established to produce new fruiting canes each year. These spurs are two or three buds long.
In blueberries, a cane fruit, the philosophy behind pruning is to constantly renew the older, decreasingly productive canes by cutting them out and forcing new canes. Plants are continually replacing old canes with new canes while most canes are in a productive, intermediate stage. For mature bearing blueberries, plants should produce at least three to five new canes per year. Start by pruning out all dead wood. Keep the three best one-year-old canes and remove the rest. Locate the oldest canes and prune out one of every six canes, starting with the oldest. Prune out all low branches and then detail prune by remove twiggy wood on older canes to increase fruit size.