Timely Pruning

PHOTO R. UNDERWOOD

When is the right time to prune my tree? This must be one of the top ten questions when it comes to the topic of tree care.
When considering the timeliness of pruning one must consider various factors. The correct timing is not always as the old adage says “when the saw is sharp”.
The first factor to consider is that every pruning cut on a living branch is an injury. Pruning wounds cause the tree to use energy to contain the decay that is inevitably caused by injuring the tree. Prune only the minimum amount needed to achieve your desired goal. Pruning excessively will result in permanent injury to the tree and increased frequency of corrective pruning in the future .
The second factor to consider is the species of the tree. Various trees have different growth patterns that affect the time of year that you can successfully prune the tree.
Trees like maple, willow and birch should not be pruned in late winter or early spiring. This will cause them to lose copious amounts of sap that will slightly weaken the trees and will make a sticky mess in your landscape. Trees that tend to lose sap can be pruned when they have fully leafed out or later in summer.
The third factor to consider is the presence of insect pests and diseases. Some trees may be made more susceptible to these problems when you injure them by pruning. For this reason species like elm and oak should only be pruned when dormant. Typically after the leaves fall and into mid winter. In many jurisdictions there are prohibitions on pruning elms and oaks during the growing season. Generally most flowering trees can be pruned right after they flower to allow new flower buds to set. Pruning these trees too late can result in poor flowering response the following year. The art of pruning apple trees is based on elements of style and timing. The art of apple tree pruning would take several volumes to cover adequately.
With many deciduous trees the later you wait to prune them in the winter the greater amount of adventitious shoots you will develop the following year. These succulent shoots are less likely to develop if the trees are pruned in fall or late summer when the trees are still in leaf. This propensity to sprout new growth is the force behind rejuvenation pruning. This pruning technique is mainly practiced on leggy declining shrubs and is not recommended for most trees. Rejuvenation involves cutting the shrub off to within a few inches of the ground and allowing it to grow back from the resultant stump. This is commonly used in willow cultivation to get large numbers of canes to propagate vegetatively. Again this process is not recommended for mature healthy trees.
Spruce trees and most pine trees can be pruned in the spring when they are putting out new growth. Generally most evergreen conifers follow this rule and should not be pruned from mid summer until fall weather cools things off. Finally, it is important that your tools be sharp and up to the job at hand. Cuts larger than ¾ of an inch should be performed with a sharp saw, bypass pruners are the preferred tool below ¾ of an inch. These few general rules will be of help, but for more specific answers to tree pruning questions contact and I.S.A. Certified Arborist.