Horticulture Magazine

How To Protect Plants From Frost In Winter

frost covering flowers and foliage in a winter garden

If you want to enjoy a beautiful and productive garden year-round, considering how to protect plants from winter frosts is important.

One of the first things we learn as gardeners is that different plants have different growing needs.

And becoming a better gardener means building up a body of knowledge about the environmental needs of different plants.

As you grow as a gardener, you will learn which plants can come through the winter months unscathed where you live, and which might need a little help and protection.

In this article, we’ll take a look at how to protect plants from frost in winter.

1) Choose Winter-Hardy Plants

winter plants growing in a timber framed box

Before we begin to look at some different solutions to keep plants safe from winter frosts, it is worth mentioning that sometimes, the best solution can be the simplest one.

For a successful winter garden, and for a low maintenance scheme that can look great in your garden year after year, it can be a good idea to simply choose plants that can withstand winter temperatures and chilly conditions where you live.

There are a wide range of fully hardy plants which will withstand winter in the UK without you needing to take any additional measures at all.

When we talk about winter-hardy plants, it is worthwhile mentioning that some will be evergreen, and remain in leaf and look good without being damaged by frosts.

Heuchera is highly tolerant of frosty conditions

Others will die back over winter, but retain happy and healthy root systems that remain undamaged by frost below the soil in a dormant state, before then bursting into life in the spring.

These (usually woody) plants have specially evolved to overwinter as underground storage organs or seeds to hide away during cold periods. [source]

Choosing the right plants for the right places might mean that you do not need to take any additional measures to protect plants from frost in winter.

It is also worth mentioning that if you have a vegetable plot or kitchen garden, exposure to frost can actually be beneficial rather than detrimental for certain crops.

Brassicas, members of the cabbage family, parsnips and other root crops, and leeks, for example – will actually taste sweeter and better after they have been exposed to freezing conditions. [source]

2) Grow in a Greenhouse or Polytunnel

a greenhouse and garden covered in frost

However, there are of course plenty of more tender plants which will benefit from winter protection.

Growing undercover in a greenhouse or polytunnel structure is one key way to protect plants from winter frosts.

Container plants can be brought inside such a structure during the winter to protect them from the cold (and wet) of winter.

And there are a range of vegetables that can be grown in a greenhouse all year-round here in the UK.

An unheated greenhouse or polytunnel can often remain frost-free over winter in the UK.

Even without additional heating, it can be a very useful addition for home growing.

A cold frame can be handy if you don’t have space for a full-sized structure.

A cold frame

For even more tender or exotic plants, you can also consider heating an undercover growing area to provide even less chilly conditions.

There are many sustainable ways to do so, including with hot water or ground-source heating, or with solar-powered electric heaters, for example.

3) Create a Frost-Free Micro-Climate

a sheltered garden protecting from wind
A sheltered garden protected from the elements

If you do not have space for, or don’t really want a greenhouse or polytunnel, there are other ways to protect plants from frost in winter.

Some interesting solutions involve thinking about how you can alter the environmental conditions in your garden to create a more sheltered, warmer, and potentially frost-free micro-climate.

Where you place plants can have a bearing on the micro-climate in your garden – especially when you consider larger plants like trees and shrubs.

Placing trees and shrubs in the right places can shelter your garden from freezing winds and protect other plants from frost.

However, it is also worth noting that to protect plants from frost, it might be helpful to make changes to the existing vegetation, to help alter the micro-climate conditions in beneficial ways.

For example, you might open up a tree canopy to the south to let in more sunlight to keep things warmer in winter, or you might create gaps in boundary hedges across a slope, to drain cold air from a frost pocket.

A frost pocket is formed by topographical features, trees and other features of the environment.

This is an area that is considerably colder than other spots in your garden in winter, gets frosty earliest, and is slowest to warm in spring.

Sometimes it is possible to alleviate these frost pockets – sometimes it is simply best to avoid planting anything which may be damaged by frosts in these areas.

Simply planting tender plants in a different part of your garden could help protect them from frost in winter.

4) Cover Plants With Row Covers, Cloches or Fabric

seedlings of cabbage covered in cloth during early spring
Cabbage seedlings

Another option to consider is covering beds or individual plants.

You can use a range of different row covers, cloches or fabric covers such as horticultural fleece or reclaimed textiles to do so.

Often, you can use reclaimed materials to make row covers and cloches that might otherwise have been thrown away.

plastic bottles covering plants in autumn
Plastic bottles are commonly used to create a ‘greenhouse-like’ effect for plants

Using milk containers as small individual cloches is just one simple example. A cane or thin branch through the handle and inserted into the soil will keep these in place.

Covering beds can be a good idea in a vegetable garden, since it will provide some winter protection and allow you to make use of your growing areas all year round.

trees in a park covered by frost protection fabric
Covers can make all the difference for tender plants

You might use row covers, for example, to protect winter sowings of overwintering peas or broad beans, root crops, brassicas, or other more hardy leafy greens.

You may be surprised by the difference a simple cover can make, and the variety of crops it allows you to overwinter in your garden.

individual plant covers
Individual ‘hot boxing’ plant covers

5) Use Mulches To Protect Plant Roots

Vegetable bed with strawberries and garlic covered with mulch
Vegetable bed with strawberries and garlic covered with mulch

Another thing to remember is that plants do not necessarily have to be covered in their entirety to keep them safe from frost.

Often, it is the roots of a plant that require winter protection, not the above-ground portion of the plant.

To prevent root damage during cold winters, thick carbon-rich organic mulches can help. [source]

Simply lay straw, bracken or dried leaves in a thick layer around the base of vulnerable, or shallow-rooted plants to keep them safe from frost in winter.

This can be a good strategy, for example, with autumn-sown onions and garlic.

Mulching well around these winter crops can ensure that they get off to a good start when spring arrives.

6) Use Thermal Mass to Protect Plants From Frost

an indoor vegetable garden
Using thermal mass for an indoor vegetable garden

Whether you are growing outdoors or in a greenhouse or polytunnel, regulating temperature and protecting plants from frost involves an understanding of thermal mass.

Thermal mass relates to the capacity of a material to catch and store the sun’s heat energy. [source]

Materials with high thermal mass like stone, brick, ceramics/clay, earth and water absorb the sun’s heat during the day – then release it slowly when temperatures fall.

This is one reason why it can be beneficial to place more tender plants beside a sunny south-facing stone or brick wall.

Moving tender container plants close to a thermally massive sunny surface could help keep them safe from frost.

Outdoors, you can also protect tender plants by placing a wall with thermal mass around them.

You might use stones or bricks as bed edging, for example.

You can also build a protective wall around tender plants using bottles or other containers filled with water, which can heat up a little during the day and keep plants a little warmer at night.

Adding thermal mass is also a good idea when building a greenhouse or polytunnel.

a spade in front of a sunken polytunnel with water irrigation
A sunken polytunnel with covering to protect against frost

You might, for example, create a sunken greenhouse, or partially earth-sheltered structure, to take advantage of the thermal mass of the soil.

You could also build a greenhouse up against a south-facing wall on your home, or even integrate a greenhouse into your home.

Clever design of an undercover growing area can help you keep it reliably frost-free without having to resort to any additional heating, even in colder areas.

If you already have a greenhouse or polytunnel, you can add additional frost protection by adding thermal mass in edging, pathways or staging.

Of course, you can also improve the insulation by adding an extra layer of plastic (or bubble wrap) inside the outer skin.

Or simply use some of the other strategies mentioned above for your plants grown undercover as well as those growing outdoors.

7) Make a Hotbed To Provide Heat From Below

a hot bed with plastic covering to keep plants warm
A hotbed garden structure

One final interesting option to consider to protect plants over the winter months is to provide a natural heat source.

Rather than introducing additional space heating, you can consider taking advantage of the heat given off by organic materials as they decompose.

A hotbed is a raised bed filled with layers of compostable materials (often straw and manure) and topped with a layer of compost or soil.

Tender seedlings and other tender plants will love the gentle heat from below.

Using a hotbed, especially in conjunction with some form of cover, can help you nurture plants through the winter months unscathed.

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