In a previous article, mca575a at summa.tamu.edu (ANDERSON, MATTHEW C) says:
>Having gotten conflicting reports from various sources, I put the problem to
>the assembled knowledge here: when is the best time of year to prune woody
>shrubs and trees?
>You've heard so many conflicting opinions because for every different
situation, there is an optimum time for pruning.
Here are a few more opinions, based on books such as Harris's
Arboriculture, Shigo's New Tree Biology, and the International Society of
Arboriculture's Arborist Certification Study Guide.
A lot of it depends on the purpose of pruning. If you are pruning out
damage or disease, the sooner the better no matter what time of year.
Shigo advises against pruning at times the tree is undergoing change,
primarily bud break and leaf drop.
Spring and summer pruning generally stimulates the production of water
sprouts. If your goal is reducing the size of the plant you are shooting
yourself in the foot. If you leave it until the late summer, you may
still get sprouts, and these will be susceptible to frost.
Pruning of heavy sap flow species such as birch and maples should be
avoided in the spring, more for aesthetic reasons than any other.
I prefer to do most structural pruning in the dormant season. As far as
this not letting the tree 'heal', trees don't heal. The wound you make
stays with the tree for life. The best a tree can do is compartmentalize
the wounded area, and limit the spread of decay. The best you can do in
pruning is prune in a manner that minimizes the amount of wounding.
Avoid flush cuts, and at the same time, avoid making topping or heading
cuts and leaving stubs. The ideal cut is just outside the branch collar
and branch bark ridge.
Don't paint your cuts, either. Wound dressings do nothing to promote
"healing" and often stimulate the growth of decay causing organisms.
The International Society of Arboriculture produces lots of good stuff on
pruning and tree care. You can often find their displays in nurseries,
or often your local utility has arborists on staff who can steer you
towards more information.
Phil Graham, Prince George, B.C.
ad327 at freenet.unbc.edu