Vermont is known for its maples and other deciduous trees that turn the forests gold, orange, bronze and red in fall. Garden shade trees need pruning and training to help them maintain a graceful, open shape and fruit trees should be pruned to maximize harvests. Though techniques for pruning are similar in any area of the country, timing is critical if trees are to survive severe winters.
Trees are trimmed to create an attractive shape, to control their height, to improve fruit production and to remove dead or diseased wood. Making each cut cleanly without leaving a long stub helps the wound to heal. Each tree has a natural branching pattern that should be enhanced rather than restricted, even when reducing height. In severe winter areas such as Vermont, removing weak branches and narrow crotches will prevent snow damage.
Vermont is one of the colder states, mainly USDA zones 3 and 4 with some zone 5 areas in the southern part. Low temperatures here range from -10 to -35 degrees Fahrenheit, with humidity low enough to damage evergreens.
Pruning, especially summer pruning, can stimulate sprouts and side shoots late in the year, an abnormal flush of growth that might not survive the coldest months.
Pruning can begin in early spring and continue until the buds begin to open. Minor pruning during active growth is fine, but major pruning will put the tree under stress. Late summer pruning can result in greater winter injury and fall and winter cuts heal more slowly and are more subject to tissue damage.
Feel free, however, to remove dead or broken branches any time and an occasional branch taken off in fall or winter won't hurt the tree. Sap oozing from the cuts in spring is normal and not an indication of harm.
Evergreen trees may show winter damage to the leaves or needles but resist the urge to prune off whole branches in spring. New growth may sprout beneath tip damaged shoots and if you wait a few months, you'll be able to asses the damage more accurately.
Hardening is a complex process that prepares plants tissues to withstand the intense cold of northern winters. It can be assisted by withholding water in late summer, by fertilizing lightly, and by pruning early in the year, not past early July.
Newly planted trees are generally less hardy than established specimens that have had time to deepen their root systems, so protect new trees by wrapping with burlap and mulching with straw. If a tree is questionably hardy, planting it beneath taller trees or in a sheltered location near the house may help it survive the coldest winters.
Sharpen tools regularly and replace pruning saw blades frequently. Sharp tools cut cleanly and wounds heal quickly if the edges are not torn and bruised, an advantage in short growing seasons. Don't use a sealant on the wound but if you are pruning a diseased tree, do sterilize your tools with isopropyl alcohol or Lysol.