Brian Minter: How and when to prune so you don’t lose next year’s flowers

I’ve never seen so much confusion over fall pruning, especially when AI and social media contribute so much nowadays.

Although gardening is an art with more than one right answer, when it comes to pruning, common sense is the best approach.

We prune our trees and shrubs to improve their health, increase productivity in terms of fruiting and flowering, and to maintain a size and shape that conforms to our landscapes. The most important issue when it comes to pruning is the timing.

By far the majority of pruning takes place when deciduous trees and shrubs lose their foliage, making it easier to observe branch structure and any disease, dieback or pest issues. Depending on the climatic zone where you live, most pruning can be done from late November until the end of February, when most new growth begins again.

One of my greatest concerns with flowering shrubs is, after a full season of developing buds, pruning at the wrong time will destroy the important colour you expect in your garden next spring. I hear this a lot from strata and condo owners whose landscape maintenance firms, working on a tight budget, prune everything at the same time once a year, even those plants loaded with buds for a spring show.

This is especially true for the beautiful Mophead or macrophylla hydrangeas. If they are pruned any time after the end of July, all the next year’s buds are cut off and the only blooms you’ll have are a few from lower buds that escaped the pruning shears. When folks tell me their Mophead or Lacecap hydrangeas never bloom, it’s simply because they are pruned at the wrong time. It’s important to understand they bloom on older stems. Since the buds develop in late summer, they must not be pruned until after blooming in midsummer.

Fortunately, hydrangea breeders have developed many new varieties that are shorter so seldom need to be pruned. In addition, they bloom on both the old stems and again on the new growth, to ensure you get to enjoy hydrangea blossoms far longer in the summer and on more compact plants.

The other hydrangeas, like the beautiful paniculata grandifloras, with their multicolored cone-shaped blossoms, the pure white arborescens, like Prover Winners’ Invincibelle series, and the quercifolias, or oak-leaf varieties all bloom on new growth the following spring. They can be tidied up now with a light pruning and an even harder cut back in the spring, keeping them more compact and producing more flowers.

All our winter and early spring flowering shrubs have already set their buds by now in preparation for a beautiful display, so no pruning now please. The best time to prune this group is in spring once the flowers are finished and when the new growth begins. This timing creates a more compact plant while the new spring growth has enough time to develop buds for next year’s blossoms.