If you're not sure if you need to protect your garden plants over winter or how to do it, this guide will help. We'll cover which plants need extra care over winter, how to look after potted plants and how to protect plants from frost in your garden.
There is a reason the Met Office website comes up at the top of the internet search on my phone. Like many gardeners, I am guilty of checking the weather forecast on a far too frequent basis. You can set this guilt aside during mid-late autumn, as this is the time of year when you should be keeping an eye on the weather, so you don't get caught out by unexpected frosts. Rather like the proverbial lobster in the pot (or should it be in the fridge?), it's easy to adjust to the mornings getting a little cooler, the evenings a little darker, without realising that nighttime temperatures are hovering around the freezing mark.
This guide will help you plan how to protect delicate plants in your garden from frosts, wet weather and cold winds. If you're not sure when to expect frosts, the PlantMaps First Frost Date map gives an indication for different parts of the country, but local forecasts and a good understanding of your garden's microclimate will give you a better heads up of when you need to take action.. For advice on winter care for specific plants, check out our dedicated plant care guides, accessed via the glossary page.
Which plants need winter protection?
Most plants in the average British garden are likely to do just fine over winter without any attention. This is a huge benefit of planting species that suit your garden environment. But this doesn't have to be a limiting factor in your garden design. Just bear in mind that if you want to grow more tender plants, you need a plan for what to do with them over winter.
As a general guide, consider protecting:
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Tender and half-hardy plants: Any species given a hardiness rating of H1, H2 or H3 by the RHS.
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Borderline hardy plants: In colder or wet parts of the UK, plants rated H4 may also require winter protection.
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Young plants: Younger plants are more sensitive than established, mature plants and may need protection, even if they're rated as hardy.
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Plants grown in containers: The smaller the pot, the more likely it is that the compost and plant roots will freeze.
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Terracotta and ceramic pots: Pots made from porous materials are more likely to crack if exposed to repeated frost-thaw cycles.
If you're unsure whether your garden plants are hardy, half-hardy or tender, you can check our product pages or the RHS website. Bear in mind that many species have varieties in different categories, so you can choose one to suit your climate. As a guide, here are some examples of common garden plants in each category:
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Fully hardy garden plants (rated H5 or higher): roses, hydrangeas, camellias, hardy geraniums, hostas, English lavender (e.g., Lavender 'Hidcote'), hardy salvias (e.g. Salvia 'Caradonna'), daffodils, alliums, echinacea, heuchera, rhododendrons, asters, phlox, and many more!
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Hardy in average winters (rated H4): agapanthus, salvias (e.g. Salvia 'Royal Bumble', Salvia 'Pretty in Pink'), fuchsias (e.g. Fuchsia 'Dollar Princess'), penstemon (e.g. Penstemon 'Pensham Czar'), Lavandula stoechas
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Half-hardy plants (rated H3): dahlias, tender fuchsias, shrubby salvias (e.g. Salvia 'Amistad', Salvia 'Black and Blue'), agapanthus, canna lilies, fuchsias (e.g. Fuchsia 'Lady Thumb'), penstemons (e.g. Penstemon 'Apple Blossom, Penstemon 'Hidcote Pink')
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Tender plants (rated H1 or H2): begonias, tender fuchsias, pelargoniums
No part of the UK is guaranteed frost-free, but inner city regions and southern coastal areas often have mild winters.
A note on microclimates and soil
While your preferred weather service is a good starting point, it can be dangerous to rely on the weather forecasts too rigidly. If your home is 100 metres higher than the weather station, temperatures could be a degree lower than forecast. Or you may live in a frost pocket – a dip in the ground where cold air gets trapped – and have temperatures drop below freezing even when forecast temperatures are higher. Understanding your garden's microclimate is key to knowing when and how to protect plants from frost.
Your soil type will also have an impact on how well plants in your garden cope with frost. Many of the half-hardy plants we grow in the UK can handle temperatures down to around -5°C as long as the soil is well drained. This is true for many drought tolerant species and plants that originate in Mediterranean countries or desert climates. It's the combination of wet and cold that's the killer for most of these plants.
This means that if your winters tend to be fairly dry and you have sandy, gritty or other free-draining soil, your tender plants are more likely to survive with little or no winter protection. Conversely, if you garden on clay, which holds onto water, these plants could die even if you protect them from frost.
How to protect outdoor potted plants in winter
Plants grown in pots are more vulnerable to frost than plants grown in the ground, and even hardy plants may need protection to prevent root damage over winter. Pots can also get waterlogged over winter, so even in mild areas, you may need to take steps to protect plants in pots during wet weather.
Here are five methods to protect the roots of plants in pots and planters over winter. Information on how to cover plants to protect them from frost comes next!
1. Move plants into a frost-free greenhouse or conservatory
Unless your garden is a winter heat trap, you'll need to move tender plants indoors over the winter. This could be a heated or unheated (but frost-free) greenhouse or an unheated conservatory or porch. While tender plants may be fine inside a centrally heated home, citrus trees and hardier plants often prefer cooler conditions.
Dahlia and begonia tubers and gladioli corms need to be stored in a dry, frost-free place over winter. They don't need light, so a garage or cellar is often a good option.
Best for: tender plants, dahlia tubers, citrus trees
2. Store plants in an unheated greenhouse or cold frame
An unheated greenhouse or even a cold frame acts as a sun trap during the day. They may retain some heat at night, but on cold nights, the temperature inside may not be much higher than outside. You can wrap potted plants for extra insulation or cover your entire cold frame with fleece on cold nights.
Plants kept under glass are protected from heavy rain and winds, so this is a useful option to prevent pots from becoming waterlogged. They will need watering occasionally, and you may need to vent greenhouses and cold frames on warmer days.
Best for: half-hardy plants, Mediterranean and drought-tolerant plants that suffer in wet, cold soil (e.g. lavender, rosemary, sedums, nepeta)
4. Group pots in a sheltered spot
If you don't have somewhere undercover, the next best thing is to group your pots together. This creates a microclimate, which can increase the air temperature around the plants and provide some wind protection. Storing pots up against a south or south-west facing wall intensifies this heat island effect and can help prevent pots from becoming waterlogged.
Best for: hardy plants, all plants if no undercover option
5. Raise pots on pot feet
You may curse the amount of watering your containers need during summer, but in winter, it's a different story. Without bushy foliage to divert rainwater, the compost in pots can quickly get waterlogged, which is bad news for your plants! All your pots should have drainage holes, and in winter, it's best to raise them an inch or two off the ground to make it easier for water to drain out of the pot.
You can buy pot feet or make your own by pouring cement into cupcake cakes and letting it harden. Alternatively, use plastic lids, flat stones, offcuts of wood or anything else you have lying around!
Best for: small pots and planters, plants that need well-drained soil
4. Wrap pots and/or plants
Plants in larger pots are less likely to suffer frost damage, so you may not have to protect them at all. If your plants aren't fully hardy or your winters are harsh then you can wrap your pots to insulate them from the cold. You can use bubble wrap, fleece, hessian stuffed with straw or another DIY solution (I cut up an old mattress protector one year). Dry materials make better insulators, so you can wrap your insulating materials in old compost bags to prevent them from getting too wet.
You can wrap smaller pots individually, but a more effective method is to group them together and wrap the whole lot together. You can stuff straw or dead bracken in between the pots for extra insulation.
Best for: trees, shrubs and large planters, smaller pots left outdoors
5. Bury pots in the ground
Soil in a natural insulator, so another option is to dig a hole and bury potted plants in the ground over winter. This is effective, but it's the last option on my list, as most people don't have empty beds to dig up and stick pots in!
How to wrap plants for winter
Winter wrapping can protect tender and borderline hardy plants that grow outdoors in winter. You may also need to wrap hardier plants in very cold or exposed locations. Wrapping is used for trees and shrubs that need insulation for the whole winter, for example, tree ferns, banana plants and bottlebrush shrubs (Callistemon).
Drive some bamboo canes or stakes into the ground around the shrub, then wrap chicken wire around these to create a support structure or use smaller sticks to create a framework. Pack dried bracken or straw inside this support, around the plant. You may want to add a layer of chicken wire or netting over the top to prevent the insulation from blowing away. Cover the top in plastic to protect the insulation from rain, but remove this during dry, mild periods to let the plant breathe.
If your plant is in a pot, you can use the same method. Wrap the pot in chicken wire or a framework of sticks and pack straw in around the plant. Cover it with a waterproof cap to keep the insulation dry.
Upright shrubs and tree ferns can be wrapped in fleece. Tie the tree fern's fronds up and pack straw around them, then wrap it all up in a double layer of fleece.
Covering plants to protect them from frost
Most garden plants don't need this level of protection, but they may need some insulation when hard frosts are forecast. Horticultural fleece offers protection from frost for plants and is the easiest way to protect plants for short periods. You can buy different weights of fleece or double up layers for extra insulation.
Avoid wrapping plants too tightly, as this can damage stems and branches, but make sure the fleece is secured, so it won't blow away in high winds. Remove the fleece once the danger has passed, so the plant can access sunlight and water.
While most fruit trees and bushes are hardy, spring frosts can damage new growth and blossoms, which can affect flowering and fruiting. Cover small trees and bushes with fleece on nights when frosts are forecast, but remove the fleece during the day. Larger trees can be harder to protect, but you may be able to roll up the fleece rather than removing it completely until the cold period has passed.
Winter protection for plants in the ground
For hardier plants, a good thick layer of mulch is all the protection they need for the winter. This is particularly helpful for plants with shallow roots, such as heucheras. Dahlia tubers left in the ground will also need a thick layer of mulch to protect them from frost.
Cloches are useful to protect smaller plants. They act like mini greenhouses and are often used to warm up the soil for planting in spring or to protect young seedlings from birds. They're not suitable for leaving in place all winter, but you may use them to cover small shrubs or plants when hard frosts are forecast or to protect winter salad crops from snow.
