Brian Minter: Pruning 101 mainly down to timing for a ‘shears’ delight

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There is a great deal of blossom loss taking place in many gardens right now. No, not the stealing of plants, but rather the loss of spring and summer blooms because many folks are busy pruning off the buds of their flowering shrubs.

Timing, as the saying goes, is everything, especially when pruning plants.

Think of it this way: Many flowering trees and shrubs have been developing buds all last summer and fall, and they are ready to provide great colour this year. By pruning them now, you are removing the source of that colour.

Unfortunately, this is not an occasional misstep.

After many years of answering questions on open-line radio, I continue to be amazed how often this issue comes up. So, here is a quick lesson in Pruning 101.

How does one know which flowering plants to prune at this time of year and which ones should not be touched? It is not as simple as it may seem.

I generally follow a couple garden rules. First, observation is key. If you see buds on your plants now, it’s obvious they should not be pruned. Second, as a rule of thumb, the earlier plants bloom in the season, the more likely they will now have their buds set to flower. Winter jasmine (Jasminum nudiflorum) and Chinese witch hazel (hamamelis) are in bloom now. Buds on forsythia and quince (chaenomeles) are ready to bloom soon.

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Hydrangeas are, perhaps, the most misunderstood of all our flowering shrubs. The most popular are the mophead types (Hydrangea macrophylla) which are full of buds now, ready to open in July. Lacecap hydrangeas fit into this same category. The problems arise most often with older varieties that have grown too large (some may be six to eight feet tall), and it seems as though they should be cut back to prevent them crowding out other plants and overtaking the garden.

Resist the temptation to prune them now. If you must prune, do so strategically by cutting the stems back just above the plump buds. The best time to prune hydrangeas hard is just before the end of July. This will allow them to flush out new growth and still have time to set buds for the following season. You will have to forego some August blooms, but at least you will have had four weeks of enjoyment.

Many of today’s new hydrangea varieties, such as the ‘Bloomin’ Easy’ and the ‘Revolution’ series, are much more compact and rebloom even if they get pruned early by mistake. ‘Revolution’ hydrangeas produce blossoms that last far longer, and as they mature they become infused with a wonderful, green pattern.

Deciduous and evergreen azaleas are in full bud set now, and even though some may be a little leggy, let them bloom out. When they finish flowering and new growth begins, then prune. Since new growth develops on their old woody stems, after blooming, they can be pruned hard to regain their shape. Over the late spring and summer, new buds will set.

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The same is true of overgrown rhododendrons. After blooming, and once new growth starts, they can be pruned rather severely. Slowly but surely, new growth will sprout. It may take them two years to fill out and set buds, but the wait will be worth it because you will have a far more compact, beautiful plant.

Lilacs, too, have their buds set now and are ready to perform. After they’ve flowered, prune back any leggy plants. Older French hybrids, like rhododendrons, may take two years to set buds, but again, having a much more beautiful plant makes the wait worthwhile. Compact Korean lilacs and the new Proven Winners ‘Bloomerang’ series, which bloom twice a year, can be pruned after each blooming and still get buds the following year.

A wide variety of viburnums have their buds set to bloom early, midway and late in the season.  One of my favourite viburnums, V. burkwoodii, with its highly scented pink to white blossoms, has buds ready to open in April, as do many of its cousins, like V. carlcephalum (the fragrant snowball). Pruning these viburnums now will deprive you of both their colour and their perfume.

Other plant families, like spiraeas, are confusing. Some of this species, such as S. arguta (garland spiraea), have their buds set now to bloom in April, while late blooming varieties, like S. vanhouttei (the bridal wreath spiraea), bloom in late June and July. The early varieties bloom on old wood stems, while the late flowering varieties bloom on this year’s new growth. This is where pruning flowering shrubs becomes a learned art.

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On the West Coast, flowering shrubs provide a sequence of colour year-round, so we need to be cautious about timing our pruning. The rules of observation, early and late flowering habits and blooming on either old growth or new growth, all apply, but nature always gives us some exceptions to keep us on our toes. The same precautions apply to all our beautiful flowering trees, like ornamental cherries, plums, crab apples and dogwoods.

Proper pruning helps preserve the life and health of our trees and shrubs. It’s the timing, however, that ensures we can enjoy all our flowering shrubs to the fullest.

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