SEASONAL TIPS

Dos and Don’ts for Winter Pruning

by Paul Gellatly, Toronto Botanical Garden Director of Horticulture

January and February when trees and shrubs are fully dormant is the best time for winter pruning. With no leaves you can see form and shape much easier than with them. Here is a list of Dos and Don’ts to make winter pruning as simple as possible.

DOS

• Always have a reason to prune; not just because you want to spend some time in the garden.

• Always use clean, sharp secateurs to prevent disease and ensure clean cuts.

• Dip your pruners/ secateurs in rubbing alcohol, or one part bleach to nine parts water, between trees, or if you are removing any noticeably diseased areas after every cut. This will help stop the spread of the disease to other parts of the tree, or other trees.

• Always be safe, wear eye protection and know your limits. If it’s a big job, consider bringing in a professional arborist.

• Remove any diseased/ damaged branches.

• Remove waterspouts (upright growing branches that form on the trunk or side branches).

• Remove suckers (shoots that develop at or near the base).

• When branches cross/ chafe, remove the less important branch.

• Always prune back to an outward facing bud.

• Prune neither too far away from nor too close to the bud. Keeping a 2.5 cm distance from the bud is safe.

• Cut so the slope is away from the bud. This will ensure any water runs off, preventing rot.

• Prune Group 3 Clematis (late summer flowering) in February by cutting them to 7.5 to 10 cm from the ground. Because these bloom on current year’s growth, if you do not remove last year’s it ends up looking very heavy and messy.

• Remove old raspberry canes, prune grape vines and remove the oldest stems from fruit bushes. Healthy younger branches produce more fruit.

• Prune Hydrangea paniculata back hard in the winter, as they bloom on new wood, to promote strong growth and additional flowers.

• Summer blooming shrubs, such as potentilla and buddleia should be pruned in the winter. Because they bloom on new growth, you can even cut them right down to the ground and they should still flower this summer.

• Major pruning on foliage shrubs, such as burning bush and barberry, should be done when they are dormant in the winter. But these can really be pruned any time except late fall. Pruning helps to flush out new foliage and allows in more light. Dormant pruning is especially important for apples, pears, crab apples and hawthorne trees as they are susceptible to fire blight, a bacterial disease.

• When thinning the canopy, start at the centre and move out to the exterior. Thin out branches that make up the dense mass in order to increase air circulation and accentuate the structure and form of the plant. Never remove more than a quarter of the plant in one season as that will promote sucker growth.

• Take lots of breaks, step back, look at the tree, watch for symmetry and form, know when to stop. You can always take more off but you cannot put it back on!

• While you are close to the trees and shrubs, inspect them for disease, and for insect issues such as gypsy moth egg masses. If you see them, help control insect issues later in the year.

Photos: Paul Gellatly

DON’TS

• DO NOT prune spring flowering shrubs – i.e., forsythia, mock orange, quince, azalea, bridal wreath spirea. They are best pruned immediately after they bloom.

• DO NOT prune Hydrangea macrophylla back, as they bloom on old wood.

• DO NOT prune spring flowering trees – magnolia, lilac, redbuds, ornamental fruit trees. They are best pruned immediately after they bloom

• DO NOT prune bleeding trees – maples, birches, dogwoods, walnuts and elms produce a lot of sap remove them now to when pruned in winter. They are best pruned in the summer.

• DO NOT prune evergreens in winter. They never go fully dormant and may suffer tip burn if pruned in the cold. They are best pruned during the growing season.