Good season for outdoor pruning
The fall season is an opportunity to tidy up hedges, trees, shrubs
We can be thankful this time of the year for a fabulous growing season.
However, with all the growth comes an opportunity to control it. We enjoy the fall activity associated with fall pruning. Cool, crisp days are perfect for more than just apple picking, after all.
Here are some Dos and Don’ts.
Hedges
By their nature, a hedge requires at least annual pruning, and this is the ideal time of year to do it.
A cedar hedge that is pruned now will look handsome until the first flush of new growth come late May. Not a bad stretch between haircuts. If temperatures moderate over the next four weeks, a short burst of new growth is possible, filling out your freshly pruned hedge for the winter.
Most other hedges lend themselves to autumn pruning privet, alpine currant, boxwood, yews – you name it.
A living hedge (vs. a financial hedge, which is not in our purview) should be slightly narrower at the top and wider at the bottom to maximize the amount of light that the hedge plants receive. This also stabilizes the plants by taking advantage of their natural growth habit: wider near the roots, narrower where young growth occurs. Our rule of thumb: when in doubt, take your cues from Mother Nature.
Pruning trees
Deciduous trees can also be pruned this time of year. Some are “bleeders” meaning, they ooze excess sap come spring when pruned in late November or in the winter, when the tree is dormant. This excess sap can attract insect and disease problems that can be avoided by pruning this time of year. Bleeders include hardwood maples, beech and birch.
First, prune a tree for shape. For instance, is your Norway maple taking up more space than you wish it to? Prune it as hard as you like, removing up to 30 per cent of its growth. If you want to encourage more top growth, prune off the lower branches.
Most amateur gardeners are timid when pruning trees and shrubs. Hydro services people often prune mature trees aggressively to keep branches away from hydro lines. We do not advocate this kind of pruning, but the lesson is not wasted: pruning “for shape” can take an aggressive approach.
Pruning shrubs
All spring flowering shrubs are suitable for fall pruning and the sooner the better, as flower buds are forming now for early flowering spirea, lilac, serviceberry and the like.
Fall flowering shrubs that have finished blooming can be pruned now, but some that are still blooming, like hydrangea and rose of Sharon, are best left until spring.
What not to prune:
We leave perennials with stiff stems standing to create winter interest. Rudbeckia, shasta daisy and all ornamental grasses (some of which are looking their best right now) respond best to April pruning. Soft tissue perennials like hosta will die down naturally, and the leaves will rot on the surface of the soil. Nothing to do there.
Our advice about hydrangea is to leave them all standing over the winter. The large, finished flower will carry some light snow as it falls and create interest in an otherwise bleak winter garden. Old fashioned Annabelle (“snowball”) hydrangea should be pruned hard, to about 5 or 6 cm high come April. All others require a light pruning come spring.
Shape vs. thinning
For generations, Canadians followed the British tradition of pruning all evergreens and shrubs for shape. The result was a lot of formal, permanent plants that were all foliage on the outside and dead or dying wood on the inside.
When pruning most shrubs, we recommend that you reach deep into the plant and prune out up to one third of the heaviest wood. This will promote more growth in the middle of the plant and a shape that looks natural, not a pyramid or large ball.
Keep your garden in topshape with fall pruning.
Mark Cullen is an expert gardener, author, broadcaster, tree advocate and Member of the Order of Canada. His son, Ben, is a fourth-generation urban gardener and graduate of University of Guelph and Dalhousie University in Halifax. Follow them at markcullen.com, @markcullengardening, and on Facebook.