9 tips for protecting your garden from frost

Photo courtesy of Roberto Sorin/Shutterstock

In parts of Canada, it felt like cooler weather would never arrive this year. In southern Ontario, a heat warning was issued on the first official day of fall. In other parts of the country—we’re looking at you, Edmonton—winter made its presence known with a late-summer snowfall.

Oddball temperature fluctuations aside, we’re getting to the point where frost is a real possibility—if it hasn’t happened already (ahem, Edmonton). You may be ready for the advent of cooler weather, so here’s how to make sure your garden is as well.

Know whether your plants are vulnerable

Usually, if plants grow naturally only in warmer climates, they won’t survive a frost. This includes tropicals and frost-tender plants like impatiens and begonias. Annuals generally won’t survive, but they may spread their seeds. Perennials may lose their foliage, but the roots will survive, meaning you’ll have new growth in the spring. Finally, fully frost-hardy plants, trees and shrubs will go dormant, but shouldn’t have trouble lasting throughout the winter.

Determine how cold can your plants go

Different levels of cold affect plants differently. A light freeze or frost, down to -2 for a couple of hours, will only hurt very tender plants. A hard frost between -4 and -2 for an extended period of several hours will damage blossoms and foliage, kill root-hardy perennials and damage crops. Finally, a severe freeze below -4 for several hours will damage most plants, largely by drying them out.

Cover stuff up

If frosty nights with warmer days are forecast, you can get a few extra weeks out of your garden if you cover up your plants at night. To start, mulch the ground (if you haven’t already), but keep it clear from the roots of your plants.

From there, use frost cloths, newspapers, straw, evergreen branches or even old bedsheets to form a protective cover over the whole plant. Don’t cover them too tightly. You want air to circulate, but make sure the whole plant is covered to retain as much radiated heat as possible. Use stakes to help elevate the covering away from the plant, and weigh the edges down to stop them from blowing away.

Cover (and uncover) at the right time

The best time to cover your plants is in the mid- to late afternoon, before temperatures drop as the sun goes down. Uncover plants mid-morning once the sun’s risen and temps have warmed up.

Cover root veggies for better overwintering

Protect your winter crops, including carrots, parsnips, beets and rutabaga, with a layer of newspaper followed by a layer of leaves. This allows these veggies to overwinter without freezing, and gives you sweet, yummy root vegetables almost all year.

But don’t cover EVERYTHING

Some hardy veggies, especially kale, brussels sprouts, broccoli, cauliflower and other members of the brassica family, taste better after a frost, as cold weather causes them to produce sugars. If you want to prolong your harvesting period for a few weeks, you can cover your autumn brassicas with row covers, but it isn’t strictly necessary.

Make sure the soil is moist and healthy

Moist soil can help protect tender plants, as heat is produced when moisture in the air condenses on plants and soil. Make sure your garden is well watered and full of organic matter to help retain moisture. Mulch will help slow evaporation as well.

Design your garden to promote frost hardiness

A south-facing slope is ideal for gardens that might get touched by frost, as it will get more sun exposure and will drain cold air better than flat ground. Surrounding your garden with trees will help stop heat from escaping from the soil, although they may reduce sun exposure, so be judicious. A stone wall against the garden can act as a heat sink, keeping plants warm by absorbing heat during the day, the releasing it at night. (Fun fact: If you have a cold frame, you can devise your own heat sink using multiple jugs of water.)

Plant the right plants

If you want your garden to last as long as possible without a ton of work on your part, pick plants that are designed for frost hardiness in your area. Native plants are your best bet. Check out your local nursery for non-invasive species that are well adapted to your area. Also consider shrubs and trees with colourful branches, like dogwood, or berries, like firethorn, to keep some colour in your garden all year round.

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