How to Protect Outdoor Plants and Trees From Frost and Freeze

According to the Manitoba Co-operator, the first step is to plant your garden with species that are hardy enough to withstand the climate in your area. Plants and trees that are native to the area generally have adapted to be able to survive the local climate, while plants that are native to tropical climates almost certainly won’t survive when temperatures drop.

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Cottage Life

says that the most vulnerable plants are those that grow naturally in warmer climates. Annuals may spread their seeds even if the plants themselves won’t survive frost and freeze conditions. Perennials may lose their foliage but the roots can survive, so they’ll grow anew in spring. Plants and trees that are fully frost hardy will go dormant and survive through winter.

There’s cold and then there’s cold, and different plants react differently to the various levels of cold. According to Cottage Life, most plants will suffer damage when the temperatures drop to below –4 degrees for several hours. Between –4 and –2 is a hard frost and can kills root-hardy perennials if it lasts for several hours. When temperatures drop to only –2 for a few hours, only very tender plants will suffer damage.

The Manitoba Co-operator says that you need to place vulnerable plants in sheltered spots in the garden. For example, plant them near a fence or to the south of a line of trees, where they’re protected from wind and still get enough sun, but not too much. For very vulnerable tropical plants, you may want to plant them in pots so than you can bring them inside when necessary.

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To adequately protect your plants against frost and freeze, you need to be prepared for these conditions. So, you need to know when they’re likely to happen. Find out what the normal times for cold spells in your area are. However, check the weather forecast daily too.

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The best way to protect outdoor plants that grow in pots is to bring them in when the weatherperson predicts frost and freeze conditions. If this isn’t possible, though, the Manitoba Co-operator suggests that you bury the pots up to the rim and cover everything with a thick layer of mulch. This is because if you leave the pot as is, freeze will enter the soil from all sides.

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For smaller, tender plants, the Manitoba Co-operator suggests cutting back the branches. Then remove the bottom from a large cardboard box and place the box over the plant. Next, fill it with dry leaves. Close the top of the box and cover it with plastic, which will make it waterproof. This creates a snug little house where the plant can stay warm.

Watering the garden before a cold spell may sound counterintuitive but moisture can actually help protect the plants. This is because moisture produces heat when it condenses.

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Healthy soil full of organic matter has better moisture-retention properties. This will help the soil retain heat too.

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The Manitoba Co-operator says that good snow cover can help retain heat within the soil. So, you can erect snow fences or let branches catch snow, which you can then use to cover the plants throughout winter. It will act in the same way that mulch does.

Mulch helps to retain moisture and heat in the soil. It also helps to moderate temperature changes. However, you need to keep mulch away from the plant roots and keep it dry, or it can cause more damage.

Once you’ve applied mulch on the ground, you can cover the whole plant. You can use a special frost cloth for this. Alternatively, old bedsheets, newspapers, evergreen branches, straw or blankets will suffice. The idea is to build a kind of tent over the plant, not letting the cover actually touch the plant, because air still needs to be able to circulate around the plant. Weigh down the sides so they don’t blow open.

According to SF Gate, using plastic to cover plants against frost can be worse than not covering the plants at all. Plastic can hold moisture against the plant, which can cause more serious frost damage. It’s also too thin to provide insulation. However, you can use it in conjunction with other coverings to keep things dry.

According to Cottage Life, the best time to cover your plants is in the mid- to late afternoon. In other words, cover the plants before temperatures drop for the night.

During the day, you want your plants to be able to take full advantage of the sun’s heat. So, uncover them mid-morning, when the sun has risen.

The Manitoba Co-operator says that too much sun can cause damage to vulnerable deciduous trees and shrubs. It can cause the plant to dry out and the bark to split. To prevent this, wrap the lower parts of the trunks in burlap.

Row covers can raise temperatures by as much as 4 degrees, according to Garden Making. They provide a thermal buffer as long as they don’t touch the plants. You can leave them on during the day, since they allow the sun, water and air to permeate.

Garden Making says that polytunnels act the same way as row covers. However, you can stretch the plastic over hoops so that it doesn’t touch the plants. You need to open the sides during the day so that air can circulate, otherwise the high temperatures and humidity can cause disease.

Cloches are like mini-greenhouses for small, individual plants. Garden Making says you can buy ones made of glass. You can also cut the bottoms off plastic bottles and use these bottles to cover the plants with. However, you should remove them in the morning.

The Manitoba Co-operator says that strong winter sunshine can damage newly planted evergreens. It causes desiccation because the root zone is frozen and the plants can’t replace the moisture that they lose. To protect them, erect a burlap screen on the south and west sides. A sturdier barrier on the north side will help protect them from wind.
Looking for more? Check out 19 ways to prepare your yard for winter in Canada.