The leaves are down, and it’s tempting to grab the pruners and tidy everything up before the snow. Some trees and shrubs are fine to prune now. Others are better left alone until late winter, and a few you should hold off on until after they bloom. Here’s the quick guide for Lethbridge.
Good to prune now
- Elms. Alberta bans pruning elms from April 1 to September 30 to help keep Dutch elm disease out. October 1 to March 31 is the only time you can prune them, so if an elm needs work, now through winter is the time. Get rid of the wood promptly, and never keep elm for firewood unless the bark is removed or it’s been properly kiln-dried or heat-treated.
- Black knot on mayday, chokecherry and other cherries and plums. Those hard, black, lumpy swellings on the branches are much easier to spot with the leaves off. Cut the branch well below the swelling, and bag or dispose of the cuttings. Don’t leave them lying in the yard.
- Fire blight on apple, crabapple, pear, mountain ash and cotoneaster. Cutting out the dead, blackened branches during the dormant season, well below the damage, keeps the bacteria from spreading in spring. Clean your pruners between cuts.
- Dead, broken or dangerous branches, on any tree, at any time of year. Heavy, wet snow will finish off weak limbs anyway, so it’s better to remove them before they come down on your roof, fence or car.
Better to wait until late winter
- Most yard trees: ash, linden, maple, birch, oak and ornamental crabapples. A calm, mild day in late February or March is ideal. The tree is still dormant, you can see the branches clearly, and the cuts start closing as soon as growth begins in spring.
- Fruit trees, apart from removing disease. Do the shaping in late winter, too.
- Summer-flowering shrubs like potentilla, late spireas and hydrangeas that bloom on new growth. Prune them in late winter or early spring.
Maples and birches pruned in late winter may drip sap, or “bleed.” It looks alarming, but it doesn’t harm the tree.
Don’t prune these now
- Spring-flowering shrubs: lilac, double-flowering plum, forsythia-type shrubs and early spireas. They’ve already formed next spring’s flower buds. Prune them now and you’ll cut off next year’s blooms. Wait until right after they finish flowering.
- Evergreens: spruce, pine, juniper and cedar. Leave them until spring or early summer, and trim only lightly. Most can’t regrow from bare, old wood.
- Heavy pruning of anything. Big cuts in the fall can stress a tree going into winter. Save the major work for late winter.
A couple of reminders
- Boulevard and City-owned trees are the City’s responsibility. If one needs attention, call or chat with 311.
- Big trees, high limbs or anything near power lines: hire a certified arborist. Never prune near power lines yourself.
For the full guide, including how to make a proper cut, the three-cut method for heavy limbs, and what to do after wind or hail damage, see our Pruning Trees and Shrubs page.
Sources: Government of Alberta Dutch elm disease rules and the STOPDED program; Gardening at USask.
— From all of us at Lethbridge Weather
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