How to protect plants from frost: 9 cold snap survival tips

We have been treated to mild winter weather so far, but as the temperatures finally threaten to drop, it’s important to act now to protect plants from frost in your garden. Do nothing, and all those months of weeding and watering, fertilising and feeding will be in vain. And come the spring, you’ll be left to fork out (if you’ll excuse the pun) on replacement flowers and shrubs.

But how can you best protect your greenery from below-zero temperatures? We’ve asked gardening experts, including horticulturist and nursery owner Sarah Raven, and bulb specialist Hannah Rowson, to give us all their best tips.

9 ways to protect plants from frost

The good news is that most of your plants will be hardy enough to survive in situ, given the right protection. However, there may be a few more delicate flowers that will need to be extracted from colder climes and reintroduced when the worst of the weather is over. We know how they feel…

1. Cover up your plants

“Protective coverings like horticultural fleece, hessian or polystyrene sheets can give vulnerable plants a better chance against winter frost,” says Hannah Rowson, assistant garden centre manager at bulb specialists J. Parker’s. “These materials are breathable and insulating, helping plants retain moisture without getting waterlogged. Wrap stems and branches securely, especially for sensitive shrubs or young trees, to prevent frost cracking.”

When it comes to horticultural fleece, I recommend Amibars Garden Fleece, which comes in a range of sizes from 1.5 x 10m to 3 x 10m.

2. Add more mulch

The plant equivalent of upping the tog rating of your duvet, a layer of mulch will help greenery survive the coldest weather by stabilising the soil temperature.

“Mulching beds and borders insulates the soil, allows plant roots to retain warmth and moisture and offers protection from frost damage,” explains expert gardener and nursery owner Sarah Raven. “Apply a thick mulch layer before the first hard frost hits, and then again when the last frost passes in spring. Tender plants like pelargoniums will be particularly grateful and will hopefully emerge from the cold in good condition.”

Hannah recommends a double mulching technique. “Start with a base layer of straw or shredded bark around the plant, then add a loose compost or leaf-mould layer on top,” she suggests. You could create your own mulch over time with a garden shredder, or a lawn mower with a mulch attachment.

Keeping the soil covered in this way has another benefit, too. “That extra protection from the wind, water and possibly even snowfall also assists in preventing water loss, and makes it much harder for weeds to grow, which will help when spring comes back around,’ reveals Andy McLaughlin, landscaping specialist at RF Paving.

3. Place delicate plants under a cloche or cold frame

For tender perennials or winter vegetables, both Sarah and Hannah recommends using cloches or cold frames. “These mini greenhouses trap warmth, prevent excessive moisture and shield plants from the cold winds that can cause frost damage,” Hannah says.

4. Dig out tender plants

Tender perennial plants like dahlias, begonias and gladioli can be lifted before the first frost. Keep an eye on the weather forecast in the run-up to winter to make sure you don’t get caught out.

“Wait until the plant has fully died back and cut the plant down to the base, carefully dig up the tuber and shake off any remaining soil,” instructs Hannah. “Check for any damaged tubers and remove those, leaving healthy ones intact. Store them in a cool, dark, dry spot, like a box or container. If temperatures drop very low, cover them with garden fleece or newspaper layers for added protection. From March to May, begin the potting process again to prepare them for replanting outdoors.”

5. Or cut dahlias back as first frosts arrive

“Recently, we’ve had milder winters in southern England, so I leave dahlias to overwinter in the soil,” says Sarah Raven. “Once the first frosts arrive, cut them back to within 10cm of the ground and cover them with a thick mound of mulch. If we have a harder winter on our hands, bring dahlias indoors to be on the safe side.”

6. Raise containers and pots off the ground

Potted plants can be particularly vulnerable in winter. Hannah advises placing containers on pot feet or tiles to lift them off the cold ground and improve air circulation. “With all the extra rain in winter months, waterlogging is one of the biggest issues as this can lead to frozen and rotten roots. Use grit, small pebbles or pieces of broken pot to add air pockets to your compost which allows rainwater to flow freely. You can also insulate pots with hessian or bubble wrap for an added layer of protection,” she suggests.

7. Move pots to an outhouse

“Move other potted plants indoors to avoid the harsh outside environment,” advises Sarah. “A shed or barn will offer sufficient shelter, but if that’s not an option, cover them in eco-friendly bubble wrap to insulate the pots and prevent cracking.”

8. Add heating to your greenhouse

It’s tempting to move plants – particularly those in pots – into a greenhouse over the winter. But if the space is unheated, it might not offer sufficient protection. “To keep a greenhouse frost-free so that you can confidently overwinter more tender plants and grow on a wider range of plants raised from seed, aim for a minimum temperature of 3°C,” says Rebecca Bevan, author of The National Trust School of Gardening.

“The best choice is usually an electric heater with a thermostat plugged into the mains, although solar-powered products are available.

“For more tender plants, such as citrus, a minimum of 7 to 10°C during winter is necessary, but this uses a lot of energy and is usually the preserve of specialist growers,” adds Rebecca. “If you do decide to heat your greenhouse, ensure the electrical work is carried out by a qualified electrician and that you use only equipment suitable for the damp, humid atmosphere. Try to restrict the space you heat by sectioning off an area and keeping all the tender plants in there.”

9. React quickly to weather changes

Hannah warns that removing covers during milder winter days can prevent rot, and then replacing them when temperatures dip again. “As the weather warms, gradually remove coverings to help plants adapt. By starting with a few hours each day, you allow plants to get used to sunlight and warmth, which reduces shock and promotes healthy growth,” she says.