Wednesday, February 4, 2009

Winter Pruning

Darcy asked about pruning mature trees and shrubs. He wondered  what to remove and when - he also wondered if there was someone who could guide him in making the right decisions.

The simple answer for Darcy is that he should minimize pruning of mature trees. By the time trees are advanced in age they are growing slowly and do not send out large amounts of new growth unless something - or someone- triggers unnecessary and sudden growth. Old trees should have been "trained" when young so will probably not need any more shaping now.

Heavy pruning of any tree in the dormant season will possibly trigger lush growth in spring so this should be minimized. Light pruning to remove an occasional broken branch, crossing branch or branch interfering with a power line can be done in our zone (3-5) while the tree is dormant (from February to mid-March) or in June after it has fully leafed out.  It is illegal in Calgary to prune Elm trees in summer so if he has an elm it could be  trimmed now but only if absolutely necessary (ie a broken branch). Before he makes any quick moves, Darcy should call an ISA Certified arborist for a consultation.  It is better to be safe than sorry. We avoid pruning of any kind once trees start to grow - ie the buds are swelling and leaves are emerging (Mid-March through to mid-May). This is a time of high energy use by the tree as it  tries to push out new leaves. 

Shrubs are an entirely different matter. A mature shrub can either be beautiful because its nature and structure have been retained over time with careful pruning or it can be a rat's nest of tangled branches after years of abuse. Sometimes it is easier to do renewal pruning (ie cut back heavily) in the late winter (Feb- mid-March) on shrubs that have become an overgrown eyesore. Avoid cutting spring blooming shrubs such as lilacs now because you will remove all the beautiful blooms Darcy!

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