Early pruning to guide growth into mechanically strong form is called structural pruning. Much like early childhood education, it is the most beneficial time to intervene in the life of the tree. Young trees pruned to eliminate weakness in the branching habit will not need nearly as much “remedial” pruning later in life. For information on structural pruning, go to: http://hort.ifas.ufl.edu/woody/structural-pruning-flash.shtml . If you are paying to have the work done, make sure the person making the pruning decisions knows these concepts and principles.
Prune initially at planting, and ideally every 2-3 years for the first decade of the tree’s time in your landscape. During the second decade, consider having the tree structurally pruned every 5 years. After this, minimal pruning should be needed if there is no storm damage or similar problem.
Mature trees that did not receive structural pruning may need to have larger branches taken off to avoid mechanical failure. Co-dominant stems with included bark zones are prone to splitting failure, which can be very dangerous if there are targets in the vicinity. For all mature trees, the bulk of pruning should be aimed at managing risk; a strongly structured tree may not need pruning for years and years. Some things to remember:
DO NOT have a tree pruned solely on the advice of someone selling pruning services; consult with the local Cooperative Extension Service office for unbiased opinions.
Do not judge the worth of a pruning job on the amount of wood the pruners removed. Less is better! In most cases, do not remove more than about 24% of the living tissue in a given year; much less on older and/or struggling trees.
Do not have interior foliage and branches removed – the tree put them there for a reason. If you prune them out, they are likely to regrow in a few years anyway, because those interior leaves are very helpful to the tree in a variety of ways.
Do not use pruning paint or sealant – it doesn’t help.
Sometimes branches need to be pruned off for clearance reasons – maybe they block traffic signs, or hang low over sidewalks. Try to see these developing and remove them early in the life of the tree. Remember that a small wound is much easier for the tree to deal with than a large wound.
Fruit trees and small ornamental trees may also be pruned to emphasize flowering and fruit production. Look up information on the particular species of tree to find the best pruning approach; we recommend looking at sites coming from universities, in particular from the Cooperative Extension Service departments at many land-grant universities.
Bad decisions on what to prune, and poorly executed pruning cuts, can reduce the structural integrity and health of the tree. If you are comfortable with gardening and landscaping, read up on the specific type/age of tree you have and make your pruning decisions based on that. If you are not sure about the pruning needs, consult a qualified, trained and reliable professional service. You can find a listing of local ISA Certified Arborists by going to the ISA website and searching by location.