Issue: August 8, 2005
Training new treesQuestion:
I just purchased a new home, and the landscaper planted five fruitless mulberry trees. Since these trees have come from a nursery, when and how should I prune them? I live on 3/4 of an acre, so on one hand a large tree is not an issue but on the other hand, I want a nice looking shade tree with a nice shape to it.
It is good that you are thinking of this now. Training a tree involves cutting smaller branches and doing less damage than trying to prune an older established tree into good form after several years. Some nurseries (not all) prune their small trees to give them a "lollipop" shape that may look good now but results in trees with all branches coming from almost the same point on the trunk. This causes problems in the future. Correcting this type of tree form should be done early in the life of the tree in the landscape. Even if the tree was not pruned to the lollipop shape, there will be some formative pruning necessary.
The fruitless mulberry is a vigorous tree and can grow quite rapidly once established if it receives sufficient water. However, this summer I would only recommend removal of damaged (skinned bark, broken) or dead branches. When removing these damaged branches, make your pruning cuts outside the branch collar (the swollen area at the base of the branch that you are removing) or cut back to a healthy bud that will grow in the desired direction (on the side of the branch in which you want growth to develop).
The dormant season (after leaves fall from the tree and before the buds swell in the spring) is the best time to do most pruning. During the first winter, you may begin pruning to remove crossing branches and branches that will grow too close to structures or block views (traffic safety or vistas). Low branches that interfere with pedestrian or vehicular traffic should be removed at this time. These lower branches help contribute to strengthening of the trunk and can be left during the first winter if they are not too large. Branches growing upward from the trunk in competition with the trunk (main leader) should be removed to prevent formation of multiple leaders which can result in branch failure (breakage) in the future.
In the second dormant season, you should select the branch that will be the lowest on the tree and remove the branches below it. Above the lowest branch, begin selecting the other major scaffold branches. These scaffold branches should be separated vertically by 8 or more inches and they should spiral radially around the trunk rather than being just above another branch. Branches that are too close to the branch below should be removed or trimmed back to minimize its growth, allowing for removal as a still small branch in the future. Branches developing as secondary leaders should be removed or cut back to an outward growing branch.
Any time (summer or winter) you see damaged branches (from wind or other factors), they may be removed immediately.
As you prune, maintain the natural form of the tree and remove as little live wood from the tree as possible. During any one season, prune so that no more than 10 to 25 percent of the twigs that will produce leaves will be removed. Removing too much of the living wood (that will support leaves) will stress the tree and can result in future problems.
There are publications available at your local Cooperative Extension Service office that may be helpful to you. They will provide pictures of what I have described in words. NMSU Extension publication H-156 (Tree Pruning Techniques) has just been revised and will be available on the internet in a month or so at http://cahe.nmsu.edu/pubs/_h.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!