Gardeners can protect their plants from October's first frost by covering them with fleece, cloches, or even an old sheet, according to David Denyer, Eflorist's flower and garden expert with over 35 years of experience.
With autumn well underway, temperatures are starting to drop considerably, and the inevitable first frost is just around the corner. Following months of warmth and growth, many plants haven't yet built up their winter resilience, rendering them susceptible to abrupt cold snaps, making this amongst the most destructive periods of the year for gardens.
Why the first frost is dangerous
Describing the first frost's hazards, David shares: "The first autumn 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."
The flower and gardening specialist further elucidates that later in the winter, most plants will naturally harden off and become more resilient, but the first frost typically arrives before they've had the opportunity to do that, which is why it can inflict such extensive damage.
How to protect garden plants from overnight frost
David says there's one crucial thing gardeners can do to protect their plants from frost overnight: "You need to slow down how quickly they lose the warmth they've absorbed during the day."
To achieve that, all gardeners need to do is cover their more vulnerable plants. David advises: "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."
The gardening expert adds: "Just remember to remove the covers again in the morning so that air can circulate and the plants can breathe. If you leave covers 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."
The plants most at risk
The gardening expert explains that the plants facing the greatest risk are half-hardy bedding varieties, such as begonias, which typically suffer first as they cannot withstand freezing conditions.
Dahlias require particular attention as well. Their water-storing fleshy tubers are susceptible to damage when frozen, causing the tuber walls to rupture, preventing regrowth the following year, the gardening and flower expert adds.
David continues: "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."
Additional protective measures to take
The gardening and flower expert says: "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 safeguarding your soil, you're simultaneously shielding your plants' roots from harm caused by repeated freezing and thawing, ensuring they remain healthier and bounce back more readily come spring."
What to avoid before first frost
David cautions: "It may be tempting to give your plants a feed in autumn 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 frequent error many gardeners make during autumn, according to the horticultural expert, is watering late in the day. While you may be accustomed to evening watering to escape the summer heat, once temperatures begin to fall, this practice can prove hazardous.
David elaborates: "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."
The flower and garden expert adds: "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."
