Pruning by homeowners can be practical for the first years of a live oak's growth. However, training live oaks to strong shapes that fit the landscape's needs can require equipment and skills that non-professionals rarely possess. Maintenance of mature trees sometimes calls for climbing gear, chainsaws and possibly even boom lifts.
Live Oak Pruning
Avoid pruning this evergreen oak in spring when the chance for fungal infection is highest. Even in the deep South, the best season for pruning will be late winter. Since oak wilt infects open wounds of live oak trees and isn't treatable, use a paintbrush to cover all pruning cuts with pruning paint immediately. Ordinary latex paint is not an acceptable substitute.
Keep pruning to a minimum until the tree grows tall enough for limbs to clear obstacles. Control any tendency for low, sideways growth or multiple trunks by pruning back limbs and unwanted vertical shoots to major branch collars or to the trunk. Live oaks grow with a spreading shape almost twice as wide as the tree's height. From 65 to 85 feet high at maturity, large live oaks can approach 150 feet in width. Planted in yards, live oaks must be trained by pruning so that their mature forms stay clear of buildings and vehicle traffic. Early pruning encourages vertical growth of a single trunk.
Remove crossed branches in the lower story of the tree and cut back smaller, overhanging limbs -- homeowner maintenance is usually limited to these tasks. Common forms for live oaks are three or more high-spreading limbs and a central leader. Upper stories of the tree can be left to a more natural growth.
Sever unwanted limbs just before the branch collar, which is a raised band of tissue at limb junctions and the main junction with the trunk. Using a pruning saw or chainsaw, undercut the branch to about one-third its diameter and then saw through from the top side. A good pruning cut should be flat, without splintering or tearing, and does not injure the branch collar. Proper pruning cuts play as much of a part in preventing infections as do pruning sealers. After pruning, use a paint brush and pruning sealer to cover the fresh wound.
Leave the selection of the main branches to a professional arborist. Live oaks may require professional pruning every five years. Live oak branches become as large and heavy as many full-sized trees. As the limbs grow outward, the branch will gradually arch downward before lifting up again toward open sky. A large branch stemming from a trunk at 20 feet from the ground could clear a building easily but dip to 15 feet as it gains length and weight. Branches overhanging rooftops may lower until they touch the roof itself.