Making a DIY Fleece Tunnel for Raised Beds

Why a fleece tunnel earns its place

Frost rarely arrives politely in a UK garden. More often you get a fortnight of mild, damp weather, then a clear night that drops to -4°C in the hollow at the bottom of the plot. Raised beds are especially vulnerable, because the soil sits above the general ground level and the roots are exposed to cold air on every side. Salad leaves, winter lettuce, land cress, chervil, parsley and coriander will shrug off a light touch of frost, but a proper pocket will blacken them overnight.

A hoop frame covered with horticultural fleece buys you two to four degrees of protection, keeps cold wind off the foliage, and stops frost settling directly on the leaves. The hoop part matters more than people expect: fleece laid straight onto plants freezes wherever it touches, so leaves in contact with the fabric suffer first. Lifting the fleece clear on a simple arch solves that at a stroke, and gives you a tunnel you can open and close in seconds.

What you need

• Blue MDPE water pipe, 20mm or 25mm, cut into hoops. For a bed around 1.2m wide, 2m lengths bend into a comfortable arc without kinking.
• Horticultural fleece: 17gsm for light protection, 30gsm for genuine cold. Buy enough to cover the hoops with slack — roughly the length of the bed plus a metre.
• Weights for the edges: timber battens, bricks, scaffold board offcuts, or simply soil from the path. Stones alone tend to lose the argument with a gust.
• A hacksaw or pipe cutter, plus short canes or 150mm lengths of rebar to anchor the hoop ends if you want extra grip.

Building the frame

Work along the bed and set your hoops at 60–75cm intervals. Push a cane or a short length of rebar into the soil about 20cm deep at each foot position, then slide the pipe over it. This stops the hoops twisting in the wind and makes them easy to lift out in spring. If your soil is loose, you can push the pipe straight in, but the cane method holds far better through winter gales.

Keep every hoop the same height so the fleece sits evenly, with the ridge about 60–75cm above the soil surface. That is tall enough for a decent crop of cut-and-come-again leaves and low enough not to catch the wind like a sail. Firm the soil around each foot with your heel, and if the hoops feel wobbly, run a length of twine along the ridge and tie it to the end hoops to hold everything in line.

Covering and securing

Choose a still day if you possibly can. Unroll the fleece over the frame and leave it slightly slack — you want a gently draped tent, not a drumskin. Pull the ends over first and weight them down, then work along the sides. Burying the edges in a shallow trench of soil is the tidiest method, but a batten laid along each side is quicker and just as effective.

On exposed plots, run twine from side to side over the top of each hoop and peg it down. Fleece tears at sharp corners and in strong wind, so reinforce the end panels with a strip of tape or use a heavier grade there. As a rough guide, 17gsm fleece gives about 2°C of protection, 30gsm around 3–4°C, and two layers of 17gsm work well because the trapped air between them insulates.

Day-to-day management

Ventilation is the part most people skip, and it causes more losses than cold. On mild, bright days, lift the sides of the fleece to about 20cm for an hour or two, usually mid-morning to early afternoon. Trapped damp and warmth encourage botrytis, mildew and leggy, soft growth that collapses at the first hard frost.

Water sparingly but do not forget it. Evaporation is much slower under cover, yet plants still transpire, so check the soil at knuckle depth every few days and water in the morning if it feels dry. Harvest little and often — cut the outer leaves and leave the heart to regrow. Check for slugs and aphids, which adore the shelter, and clear any fallen leaves before they rot.

In a severe spell, add a second layer of fleece or a sheet of bubble wrap over the top, then remove it as soon as the thaw arrives. By early March, start hardening plants off: peel the fleece back during the day, cover again at night, and after a week or so you can take it off altogether and sow your first successional salads.

Small snags to plan for

• Sagging between hoops — close the spacing to 60cm or add a twine ridge line.
• Tears at the corners — reinforce with tape or double up the fleece at the ends.
• Wind lifting an edge — always weight the windward side first, then the leeward.
• Frost pockets — a bed at the bottom of a slope or tight against a fence runs colder, so use 30gsm there or add a second layer.

Look after the fleece and it will last several seasons. Shake it dry, roll it rather than folding it, and store it somewhere dark and rodent-free over summer. Come next autumn, the frame will go back in within ten minutes and you will wonder how you ever gardened without it.