Protecting a vegetable garden from frost: what to cover

When frost is forecast, first identify what is actually vulnerable: a tender crop recently planted out, an exposed young plant and an established crop suited to the season do not need the same response. Check the local forecast and the bed's exposure, then choose a cover you can secure properly. Fleece can soften the cold, but no stated temperature figure guarantees that every plant will be safe.

Which crops should you protect first?

A late spring frost mainly threatens tender plants recently moved outdoors: cover them or bring pots inside if practical. At the first autumn frost, also consider whether the crop is nearing the end of its cycle. Picking usable fruits before nightfall may be more worthwhile than extending a whole bed; reserve covers for crops you still intend to keep growing. The two situations call for different levels of effort.

Prioritise tender summer vegetables still outdoors, including courgettes, tomatoes, beans and peppers, especially soon after planting. The RHS describes these tender crops in its UK context; frost can damage their soft leaves and set back a young plant. Established crops adapted to the season need a different assessment. Do not cover the whole garden by instinct: list the plants at risk, their stage and the parts that your cover can actually shelter.

Conditions can differ within one garden. A sunken bed, a wall that releases warmth, a windy passage or a low hollow may behave differently even over a short distance. The RHS guide to assessing garden microclimates describes British gardening conditions; observe your own plot rather than deriving a universal planting date. Marmanda's guide to when to plant tomatoes also explains why frost risk has to be judged locally.

Fleece, a tunnel or ground cover?

Fleece over hoops can reduce direct exposure and shelter plants from wind. Secure its edges so it cannot blow away or rub against leaves. A tunnel offers a more structured shelter; choose a stable design suited to the area you need to cover. Ground cover can protect the soil and low parts of a crop; it may not shelter foliage. Choose by crop height, the area to cover and whether you can put the protection in place before nightfall.

The RHS suggests that some heavier fleeces give roughly 2 °C of protection. That figure refers to certain products; it is neither a safe minimum for every crop nor a promise for your garden. Performance depends on the material, how it is fitted, how long the cold lasts, wind and exposure. On a cold night without solar gain, temperatures under cover can approach outside air temperature. The RHS guide to fleece and crop covers sets out these limits in its own gardening context.

How should you set up a cover?

Put it in place before the cold arrives. If hoops are available, avoid pressing fabric onto foliage. Check the anchors and edges, and make sure water cannot pool on a tunnel. If you use more than one layer, secure them without crushing the plant. Open or remove protection when conditions become mild again so heat does not build up and air can circulate. Do not leave a cover in place without checking it.

What if the protection may not be enough?

If the equipment cannot cover an entire plant or the forecast exceeds what you can reasonably shelter, focus on the most vulnerable specimens and avoid adding loose, poorly secured layers. A potted young plant may be moved temporarily to a sheltered place; a crop rooted in open ground cannot. After the cold spell, inspect before removing damaged leaves: wait until you can distinguish living tissue, then resume ordinary care as conditions allow.

Planning can help you identify tender crops and their positions in advance, but it cannot replace a forecast or suitable protection. For other seasonal tasks, see the vegetable sowing and planting calendar. The useful outcome is a proportionate decision that you monitor, not a promise that fabric will cancel frost.