TO PRUNE OR NOT TO PRUNE, WE ANSWER THE QUESTION
As the last of our fall colour disappears, the orchestration of next spring ’s garden can now begin.
Timing is everything when it comes to resizing our plants. Once the foliage comes off our deciduous trees and shrubs, the opportunity to prune has arrived. The window for pruning deciduous trees and shrubs is roughly from mid-November until the end of February, and in colder regions well into March and April.
With our busy schedules and often inclement late fall and winter weather, we can’t always choose the ideal time to prune. In our own gardens, when suddenly every tree and shrub decided to spurt lots of new growth, I phoned the late Gerald Straley for some advice. At the time he was the plant guru at UBC Botanical Gardens, and he explained that, in reality and in many situations, you have to prune when you have to prune, even though the timing may be wrong. He assured me that plants will generally recover nicely.
With that in mind, the main rules I try to follow are those of Mother Nature. By observing the habits of plants and understanding how and when they grow, flower and produce fruit and berries, you begin to learn the best ways to grow and contain them.
Flowering shrubs are, perhaps, the most confusing when it comes to pruning. It’s all about when they form their flower buds for next year’s blooms. That’s the key.
Take, for example, the macrophylla hydrangeas: the ones that have big mop heads or lacecap blooms and create stunning displays in midsummer. They form next year’s buds from late July through September. Many folks wait until the leaves fall off these large-growing varieties before giving them a hard pruning to keep them more compact. By doing so, they eliminate most of next year’s blossoms. The best time to prune, while still ensuring the development of new buds for next year, is the end of July, even though they may still be flowering. The newer varieties, like the “Everlasting Series” I wrote about in July, also produce on new growth, so they can be pruned later and still have blooms next summer.
All the arborescens types of hydrangeas, like the old “Annabelle” and the newer “Invincible Series,” set buds on next year’s growth, so no problem pruning in late fall and winter. The same is true of all PeeGee hydrangeas (H. paniculata ‘Grandiflora’) that have those big, beautiful, cone-shaped flowers; so again, no concerns if you prune in fall and even in early spring.
At this time of year, the flower buds are already formed on winter-flowering shrubs such as viburnum ‘Pink Dawn,’ evergreen and deciduous azaleas, corylopsis, witch hazels, rhododendrons, camellias, forsythias, flowering quinces, daphnes, kerrias, flowering currants and lilacs, to name just a few. So, don’t prune them now! Typically, you prune them just after the blooms are finished for the season and when the new growth begins.
Late-flowering shrubs like buddleias, deutzias, hibiscus, beauty bushes, kolkwitzias, flowering elderberries and spireas all set bud and bloom on new growth and can be pruned even when the new growth begins in early spring. Rose pruning is a little different.
For the more tender hybrid teas, floribundas and grandifloras, all you do is tidy them up for winter by cutting them back about one-third their size, removing old, dead and diseased wood and applying mulch at least 30 centimetres over the bud unions to protect the growth just above the graft. This prevents winter winds from damaging them and keeps heavy frosts from freezing them down to the graft.
Tree roses need to have their stems protected up to and around the grafts with a protective wrap with insulation inside. Hardy roses, like rugosas, can be pruned now, but I always wait until the close of winter as a precaution.
Climbing roses will look far better and bloom more profusely next spring if you choose four to five of the best canes that grew this year, attach them to an arbour or fence at two-metre lengths, and then cut back everything else.
On all flowering trees, the flower buds are already set. I know that sometimes the only window you have for pruning is in winter when these trees are dormant, and you can do so, but you would lose many of the beautiful blossoms. The tree, however, would still be fine.
West Coast dogwoods don’t take kindly to pruning, but if you must, I would prune just after they bloom when they seem to respond with less dieback and risk of disease. Lilac trees, too, are sometimes reluctant to produce buds after pruning. If they need to be trimmed, next spring, after the lilac finishes flowering, selectively prune half the plant. Then the following year, prune the remainder of the lilac.
Medium-sized and larger deciduous trees, although they provide privacy and shade, also need to be pruned, both for strength in wind and ice storms and to control diseases. It’s important to maintain the natural shape of the tree while keeping it at a manageable size.
Our beautiful Japanese maples struggle with long, wet winters and are especially unhappy with wet feet. I have found it best to prune them in spring when the growth becomes quite active. They seem to recover more quickly and with minimal dieback.
The other anomalies are birch and walnut trees. Just by their nature, the very best time to prune them is in mid-July.
Most evergreens can be pruned anytime of the year except during extreme heat or cold. Pine and spruce trees, however, are usually pruned after the buds and candles pop in late May and June. When pruning cedars, try to keep them slender to minimize snow damage, but at the same time stay within the ‘green’ wood because they don’t send new growth out of older, hard wood.
Fast-growing broad-leafed evergreens, like laurels and photinias, can be pruned now or left until spring. Azaleas, rhododendrons and camellias are all budded now and are generally pruned after they flower in spring when the new foliage growth begins.
As our herbaceous perennials begin to look tired and their green foliage has turned brown, it’s time to clean them up by simply cutting them off at ground level.
Vines, too, should be tidied at this time of year, especially any wild late summer growth. The woody stems of wisterias, climbing hydrangeas and early-blooming clematis like the montanas, now have their buds set, so just a tidy up is required.
Prune mugo pine candles in half in late May to mid-June to maintain a compact and dense shrub, but most evergreens can be pruned any time of year, except in extreme heat or cold.
The woody stems of wisterias now have their buds set, so just a tidy up is required at this time of year along with climbing hydrangeas, early blooming clematis and vines, especially any wild late-summer growth.