Protecting Winter Crops with Fleece and Cloches

Why Winter Protection Earns Its Keep

British winters are rarely about brutal, endless frost. They are about wet, wind, and the sort of damp cold that seeps into a plant and rots it from the roots up. A January that swings from mild, drizzly days to a sharp -5°C night is far harder on winter vegetables than a steady cold spell, because plants never get the chance to harden off properly.

That is where a bit of simple protection pays for itself many times over. Fleece, cloches and cold frames do three jobs at once: they lift the temperature by a few precious degrees, they keep battering wind and heavy rain off the leaves, and they stop the soil around the roots getting waterlogged and frozen solid. On my own plot, an unheated frame or a fleece-covered row will happily carry winter salads, chard and parsley through to March, while the uncovered rows sulk, yellow and give up.

Getting to Grips with Garden Fleece

Horticultural fleece is the workhorse of winter growing. It is lightweight, lets rain and air through, and is cheap enough to buy by the metre. The thickness is given in grams per square metre, and that number matters.

• 17–20gsm fleece is the everyday choice. It gives roughly 2–3°C of extra warmth and shrugs off light frosts, cold wind and driving rain. Ideal for winter salad leaves, spinach, chard, spring cabbage and late sowings of hardy herbs.
• 30gsm fleece is the heavier grade for properly cold nights and exposed, windswept plots. Use it over overwintering broad beans, young kale and anything you are pushing slightly beyond its comfort zone.

The single biggest mistake is draping fleece straight onto the leaves. In a hard frost the fabric touches the foliage and the cold passes right through, and worse, the weight of snow can crush plants flat. Instead, run hoops of blue water pipe, or push in short canes topped with old tennis balls, and lay the fleece over that. Leave the sides loose enough to lift on mild days, and always weight the edges down with bricks, stones or lengths of timber — a gale will find any gap and turn your fleece into a parachute.

Do lift the fleece on mild, bright days. Trapped damp air under a cover is a recipe for botrytis and mildew, and pollinators need access to any early flowers on broad beans.

Cloches: Old Ideas, Still Brilliant

Cloches suit small plots and raised beds beautifully, because you can cover a plant or a short row without committing the whole bed. Glass bell jars look lovely and last a lifetime, but plastic tunnel cloches are cheaper, lighter and far less heartbreaking when they crack.

You can make your own in ten minutes with a length of water pipe bent into an arch and a sleeve of polythene, or by cutting the bottom off a large plastic bottle and popping it over a single lettuce. Cloches are perfect for bringing on early carrots, protecting a few lettuce hearts, or sheltering a newly planted batch of winter greens while they establish.

Ventilation is everything. On a sunny February afternoon the temperature inside a sealed cloche can climb high enough to cook the plants within an hour. Prop the ends open on any mild day, and close them up again before dusk. Keep cloches secure with a cane pushed through each end or a brick on the rim.

Cold Frames and Their Quiet Magic

A cold frame is simply a bottomless box with a sloping, transparent lid, and it is the most versatile piece of winter kit you can own. Site it against a south-facing wall or fence to soak up reflected warmth and shelter, and set it on a base of gravel or rubble so it drains freely.

Use it for:

• Overwintering pots of mint, thyme, rosemary and bay that would otherwise sulk in the wet.
• Keeping winter lettuce, land cress, corn salad and rocket cropping through the coldest weeks.
• Hardening off spring-raised seedlings before they go out to the allotment.
• Rooting cuttings and storing a few tubers or bulbs in pots of dry compost.

Prop the lid open a finger's width on all but the coldest days. A cold frame that stays shut for a fortnight will grow more mould than plants. Water sparingly — a little in the morning, never in the evening, and never when the compost is already damp.

Matching Protection to the Crop

Not everything needs covering, and over-protecting can do as much harm as neglect.

• Fleece over hoops: winter salads, spinach, chard, parsley, spring cabbage, young broad beans.
• Cloches: individual lettuce, early carrots, newly planted winter greens, sweet peas overwintering.
• Cold frame: herbs in pots, cut-and-come-again leaves, seedlings being hardened off.
• Nothing at all: leeks, parsnips, kale, purple sprouting broccoli, garlic and winter onions, which are all tough enough to take what Britain throws at them.

The Weekly Winter Walk-Round

Winter gardening is mostly about small, regular checks rather than big jobs. Once a week, walk the plot and shake any snow off covers before it becomes heavy enough to snap hoops or crush leaves. Firm down loosened fleece after windy nights, and check that cloche ends and frame lids have not blown open. Slug patrol matters more than ever, because slugs love the damp, sheltered world beneath a cover, so go out with a torch after rain and deal with them.

Water only when the soil under cover is genuinely dry, and always in the morning. Above all, be ready to open things up on a mild day and batten them down again by teatime. That simple rhythm — cover, ventilate, secure — will carry your winter crops through to a much earlier, far more generous spring harvest.