City Gardener: The merry frosts of May

So far, spring 2026 in Ontario has turned out to be unusually cool, even cold. But you — and your plants — can weather it

Published May 15, 2026  •  3 minute read

Many garden perennials, like these strawberry plants, will tolerate a light frost surprisingly well, especially with a little help.

I’ve been gardening long enough to know that May can frustrate the most seasoned gardener. It’s a bucking bronco of a month, bordering on heat wave one day and flinging snowflakes the next. And earlier this week, there was yet another frost warning in my area.

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It’s almost an article of faith — at least here in southern Ontario — that you should never plant before Victoria Day. But I’ve blithely, and successfully, broken that rule for years.

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I usually start putting in begonias, impatiens and pansies around the last week of April, and by the middle of May, I’ll be looking for spaces to cram in the new perennials I’ve impulse-bought at the nursery. Hey, if they’re selling them, why shouldn’t I plant them?

Early-season planting has some real advantages, chief among them that it gives young plants a head start on the growing season. They’ll have more time to set a sturdy root system and may even start blooming earlier. Besides, my existing perennials are now well up, so obviously they never got the memo about Victoria Day.

Truthfully, there is a downside to planting early, of course, and that’s the risk of a late May frost. But it needn’t be a death sentence for your new babies or really even cause any serious concern. As any good farmer will tell you, you just have to keep an eye on the weather.

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If the temperature is predicted to drop below about 3 or 4 degrees Celsius — whether there’s a frost warning or not — that’s when you need to spring into action.

First, give everything a good watering, ideally with lukewarm water from a watering can. Then, if you haven’t already, add a generous layer of mulch around the base of the plants, leaving a gap about one or two inches away from the stems to avoid rot.

Once you’ve done that, take some old bedsheets or pillowcases and lightly cover the newly planted bed, being careful not to press the sheets down too tightly on top of the young plants.

Secure the edges with stones, bricks, cans of food or anything that will hold them in place; this not only prevents the sheets from blowing back but stops cold air from seeping in underneath.

Some gardeners cover their beds in plastic or black garbage bags, but I stopped doing this some time ago. It’s not only bad for the environment (and looks terrible), but plastic doesn’t breathe, so it can overheat and even smother the plants underneath. Moisture can build up under the plastic too.

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If you have planters or window boxes, or you’ve put houseplants outside on your deck for some fresh spring air, bring them inside for the night, assuming you can move them. (If you can’t, wrap or cover them in bedsheets as well.)

My sister picked up a technique online years ago that works for small plants and even seedlings. Cut a 1-1/2 litre pop bottle in half and up-end it over the plant.

Both halves are usable: the lower half makes a perfect mini-cloche, while you can remove the cap from the upper half to allow for increased air circulation.

The next morning, once the sun is up and the air is beginning to lose its chill, gently remove the sheets and let the sun warm the plants. Unless it’s been a really killing frost (several degrees below zero), your green friends will should come through just fine.

And take heart — as I write this, it looks like a good stretch of fine spring weather is on the way at last.

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