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While some may believe that summer is the time to care for trees, year-round attention is necessary to help maintain our leafy friends as healthy assets, season after season.
Planting: Autumn is an excellent time to plant most trees and shrubs. Planting success is generally high during this time. Roots will continue to grow until the ground freezes, but wait to plant until after the leaves have dropped.
Fertilizer: Contact your local University of Wisconsin-Extension office, and have your soil tested. If a deficiency exists, use a slow-release fertilizer in early autumn. Fertilizer absorption by the tree is highest in fall, when soil is warm and moisture is readily available.
Pruning: Winter is an ideal time to prune most trees. Deciduous trees (trees that lose their leaves) are easier to prune when the leaves are off, as branch structure is clearly visible and you can better visualize the impact of removing a given branch.
Pruning during the winter is especially important for trees susceptible to insect/disease problems that are active during the growing season. For example, oak trees should not be pruned from bud break until the leaves are fully expanded (April 15 to July 1) to reduce spread of oak wilt.
Flowering ornamental or fruit trees that set their flower buds on the current season's growth are also best pruned in the late winter/early spring before shoot growth begins.
Hazard assessment: Winter is an excellent time to examine large shade trees since the bare tree affords a clear view of the trunk and branch structure. Examine the tree trunk for signs of abnormal growth, cracks, or fungal fruiting bodies (mushrooms). Inspect branch junctions for cracking. If in doubt, call a certified arborist to conduct a thorough tree hazard evaluation.
Planting: Early spring (before the trees have leafed out) is also a good time to plant trees. If possible, avoid planting on extremely hot, dry and windy days to reduce water stress on the trees.
Tree wrap: If the tree was wrapped for winter protection, remove tree wrap. This wrap interferes with photosynthesis, which can occur in the bark of young trees.
Construction damage protection: Construction season is on its way. If home construction or additions are on your "to do" list, protect your trees from soil compaction and grade change before the bulldozer arrives. Fence and mulch out to the drip line to safeguard the tree's sensitive root system (see "Building for growth" on page 13).
Insect and disease problems: Contact your local UW-Extension office or certified arborist for diagnosis assistance and treatment recommendations.
Irrigation: It is important to insure that newly planted trees are receiving adequate water (about one inch per week) throughout the summer.
If supplemental irrigation is required, it is best to apply water slowly.
Pruning: Summer is a good time to perform light pruning on most shade trees. Low-hanging branches may be thinned or reduced in length to decrease end weight and lift the canopy. Care should be taken not to remove more than one-quarter of the total foliage when pruning live wood from a tree. In summer, dead wood is easy to identify and should be removed from the tree. Removing dead limbs is important, as they can harbor insects and disease-causing pathogens.
Flowering ornamental or fruit trees that flower on shoots produced the previous growing season (e.g., crabapple, magnolia, serviceberry and lilac) should be pruned in summer, immediately after the blossoms have dropped, so that flower display is not reduced.
Storm damage: If limbs break, prune back to the trunk or to a side branch. A clean cut (outside the branch collar) is important.
Wounds should not be treated with tree paint or any other substance. Research indicates it's best to let the wound dry naturally. However, pruning wounds made between April 15 and July 1 to repair storm-damaged oaks should be treated immediately with pruning sealer.
If the tree has been struck by lightning, wait at least one month before doing any major repair work. Take care of immediate hazards, and wait to see if the tree will survive before performing other work.
A tree that has lost major branches may still be alive, but more prone to breakage. Again, call a certified arborist for an assessment.
A note on mature tree care: Pruning large, mature trees is demanding and often hazardous work that requires specialized skills and equipment. To have this work performed, please contact a certified arborist who offers this service (See "Choosing an Arborist").