The first frost arrives before plants have had a chance to harden off and become more resilient to the cold, leaving them very vulnerable
A fresh Met Office forecast has revealed that much of Britain will see cooler conditions, with overnight frost anticipated by the weekend. Yet following an ‘exceptionally warm’ November, numerous plants may not have built up their winter resilience, making them susceptible to the predicted cold weather.
Eflorist’s flower and garden specialist with more than 35 years of expertise, David Denyer, clarifies why the initial frost is frequently the most hazardous, which plants face the greatest threat, and how to safeguard your garden economically.
David said: “The first frost often catches gardeners off guard because it arrives while your garden still looks full of life. Many plants have been putting out new growth after a warm summer and wet September, but that growth is full of water and has soft cell walls.
“When frosty temperatures arrive, the water inside your plants freezes and expands, rupturing those cells and leaving them blackened and unable to recover. Later in winter, most plants naturally harden off and become more resilient, but the first frost usually arrives before they’ve had the chance to do that, which is why it can cause so much damage.”
Plants facing highest frost risk
David explained: “Half-hardy bedding plants, like begonias, are usually among the first to suffer because they can’t tolerate freezing temperatures. Dahlias are another one to keep an eye on. Their fleshy tubers store water, and once that water freezes, the tuber walls burst, which means the plant won’t regrow next year.
“Plants in pots are also much more at risk than those in the ground because the soil in containers cools and freezes faster. Garden soil acts like a layer of natural insulation, while roots in pots are left exposed to sudden temperature changes, especially if they’re in terracotta or thin plastic containers. Even hardy perennials can struggle if their roots are exposed to freezing conditions.”
How to shield your plants during the night
David advised: “To protect your plants from frost overnight, you need to slow down how quickly they lose the warmth they’ve absorbed during the day. Covering your more vulnerable plants with fleece, cloches, or even an old sheet will trap a thin layer of warmer air around them and stop it escaping overnight.
“Just remember to remove the covers again in the morning so that air can circulate and the plants can breathe. If covers are left on during the day, moisture can build up underneath, leading to rot and mould.
“For potted plants and hanging baskets, move them up against a wall where possible. This is because brick and stone walls hold onto warmth during the day and release it slowly at night, which can help raise the temperature around your plants by a few degrees, which is often enough to stop frost forming.”
How protecting your soil can be beneficial
David said: “Frost doesn’t just harm what you can see above ground, it can also damage the roots below. Adding a mulch of compost, bark, or even fallen leaves around the base of your plants helps to insulate the soil and keep moisture and temperature levels steady.
“This is especially useful for shallow-rooted plants, like primroses, which sit closer to the surface and are more exposed to colder temperatures. By protecting your soil, you’re also protecting your plants’ roots by preventing damage from constant freezing and thawing, which means they’ll stay stronger and recover more easily in spring.”
What not to do before a frost
David: “It may be tempting to give your plants a feed to keep your garden full of colour, but doing so right before a frost can actually do more harm than good. Fertilisers encourage soft new growth that may look healthy but freezes very easily, so it’s best to stop feeding after summer.
“Another common mistake that many gardeners make is watering late in the day. You may be in the habit of watering in the evenings to avoid the summer heat, but once temperatures start to drop, this can be risky.
“Wet soil conducts cold much faster than dry soil, which makes it more likely to freeze in low temperatures. If you need to water your plants, do it early in the morning so that any excess moisture can drain away before the temperature drops again overnight.
“And if your plants are caught by a sudden frost, try to resist the urge to prune them straight away. The blackened leaves might look untidy, but they actually act as a protective layer for the rest of the plant, so it’s best to wait until the weather returns to normal before tidying them up.”
