Published on Wednesday, 30 November -0001 00:00
By Janelle Daberkow, U of M Extension
A common question that comes up this time of year is, "When is it time to prune our trees?" This is actually a common question throughout the entire year, and the answer to this largely depends on the type of tree or shrub you are intending to prune.
Mid-February through the first week in April is the recommended time to prune fruit trees. This time is known as the late dormant season. Pruning during this time minimizes the possibility of fireblight in crabapples, apples, and pears, as well as minimizes canker diseases in plum and cherry trees. When pruning during spring and summer months, the chance of infection and spread of diseases by insects increases. Autumn or early winter pruning is likely to result in drying and die-back at pruning sites. Also, pruning too early in the dormant season leaves the potential for wounds to crack and dry out which delays the healing of the wound. Pruning fruit trees during the late dormant season reduces the potential disease spread and branch die-back. Pruning during this late winter time also promotes rapid wound closure when pruned prior to shoot emergence, and allows the pruner to see the tree's structure, having no leaves present during these months. Other trees such as oaks, ash and elms can also be pruned during this late dormant season.
Some trees such as maple, walnut, honeylocust and birch are "bleeders" when pruned in late winter or early spring. This oozing sap is annoying when it drips on cars and sidewalks, but there is no conclusive research that supports it being harmful to the tree. If this sap flow is a concern, prune these species in early winter, or after they have leafed out in spring. If it is necessary to prune these trees during this time of year, they should be fine, if they have no more than one quarter of their canopy removed.
When pruning, it is important to use strong, quality, and well-sharpened tools. Quality equipment when cared for properly can last for many years. Making an investment into proper tools is a wise choice. The home gardener would not go wrong having these three basic pruning tools: a pair of lopping shears, a pair of pruning shears, and a good pruning saw. Use these tools as they are directed, and be sure to keep them sharpened and cleaned after use.
Pruning is a great way to promote plant health, improve plant appearance, and keep up with plant maintenance. Start pruning your fruit trees by removing any broken, dead or diseased branches. Cut out any thin or weak wood and remove branches that droop because of heavy weight loads of fruit from previous years. Removing these types of branches will go a long way to promoting air flow and light penetration through the tree and improve plant health. Remove branches that have narrow or weak crotch angles, as these branches are more likely to split over time. When heading back branches, it is important to cut just before a bud on the upper side of the branch, so that the branch that develops will grow upward rather than downward. When removing branches, make cuts as close to the trunk or branch as possible, but just outside of the branch collar. The branch collar is the swollen area around the branch where it attaches to the tree. Cutting outside of the branch collar is important so the stem tissue is not injured. This allows the tree to seal itself in a short amount of time and have the least amount of surface area disturbed as possible. Flush cutting against the trunk will impair the new tissue and the wood will heal slowly. Never leave large stubs, as they encourage rotting into the heartwood of the tree. To prevent torn bark and wounds when removing large branches, first undercut the branch about half way through at a foot from the trunk. Then cut from above at a point an inch or two from the undercut, and finally cut off the stub that remains. Consider hiring a professional to prune large trees as it can be a very difficult and a potentially dangerous job for a single or inexperienced person.
Finally, what about the wound-dressing question? Research has shown that wound dressings are not advantageous and may actually slow the formation of callous tissue that provides a seal over the wound. Trees do better healing themselves than when a paint or dressing is applied to a pruning site. An exception to this is oak trees that must be pruned during the growing season. Such wounds should immediately be covered with two coats of a latex paint or shellac to discourage sap beetles from visiting the wound. Sap beetles, as their name indicates, are attracted to the fresh sap and may be carrying the oak wilt fungus.