Pruning 101: September is the best time to get this done!

I receive many questions from gardeners on the subject of pruning. Perhaps we know instinctively that this is an ideal time of year to get many of our plants under control and to encourage a raft of fresh new blossoms next year by pruning in early fall.

Here is a rundown of how to prune and why you should bother in September:

1. Perennials

As your perennial flowering plants (technically ‘herbaceous perennials’ vs. ‘woody shrubs’) finish their flowering cycle they are busy pushing the limited energy from their roots into seed production. This is, after all, the primary purpose of flowering in the first place. Fact is, Mother Nature created flowers to attract pollinators, not so that we can pick them to put on the kitchen table. Once pollinated and fertilized the flower matures into its seed production phase.

Remove the spent flowers and flower stems of daylilies, Veronica (Speedwell), Shasta daisies and virtually all perennials that have finished flowering this summer. With some luck you will get a ‘reflowering’ period later in the season. Do not cut them down to the ground: just the flower and several inches of stem will do.

2. Roses

I remove the spent flowers and a few inches of stem after they have flowered. I have been doing this since the first ‘crop’ of flowers finished in late June. September becomes a great time of year for a second showing of blossoms. When they are finished I let the plant stand as is all winter unless it is over one metre high, in which case I cut them down to about 80 cm to prevent them from ‘whipping’ in winter winds and risking a break at the root zone of the plant.

3. Flowering shrubs  

Much like perennials, it is best to remove the spent flowers of lilacs after they bloom to maximize the blooming potential next year. However, this is not a practical suggestion for large plants so forget it if you didn’t do this earlier this year. However, this is a great time of year to get flowering shrubs under control that have already bloomed. Like perennials, flowering shrubs lend themselves to pruning for several weeks after blooming.

If you have shrubs that are gangly, out of place or just generally taking over where they have no business doing so, this is a good time to show them your hand and get pruning. Often I find new gardeners timid about this job but I assure them they need not be. Take up to 1/3 of the growth off a woody shrub without fear that you are damaging the plant. Of greater importance is HOW you prune your shrub. I am not in favour of the ‘bowl cut’ approach and thankfully I see less of this in most landscapes. This is where the homeowner shapes and sculpts a shrub into formal shapes like round balls, squares, ovals and what have you.

Much more effective is the practice of pruning individual stems from the plant by reaching into it with a sharp pair of hand pruners and removing one stem at a time. This will open the shrub up to sunlight and improve the air circulation. New growth will occur from the centre of the plant where it will rejuvenate the plant and encourage new blossom buds to develop this fall.

‘Hand pruning’ may take more time than the ‘bowl cut’ approach, but the results are much more satisfying and of greater benefit to the health of the plant in the long haul.

Mark Cullen appears on Canada AM every Wednesday morning at 8:40. He is the Lawn and Garden expert for Home Hardware. Sign up for his free monthly newsletter at www.markcullen.com