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How to build a cold frame

A low box with a clear lid - somewhere between indoors and out. Use it to harden off seedlings before they go in the ground, start sowings early in spring, and keep salad going into winter.

• DifficultyMedium
• Time2-3 hours
• Sizeabout 120 x 60cm
• Rough costabout £66

What you need

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Tools

• Saw
• Drill or screwdriver
• Tape measure and pencil

Step by step

1. Cut the boards: 3 lengths of 120cm (two for the back, one for the front) and 4 of 60cm for the sides. Cut the top side boards on a slant, so the box is 30cm high at the back and 15cm at the front.
2. Cut 4 corner posts from a batten: two 30cm (back) and two 15cm (front).
3. Screw the boards to the posts to make a box - two boards high at the back, one at the front, the slanted ones at the sides.
4. Make the lid: screw battens into a 120 x 60cm frame, then screw the polycarbonate on top. Drill holes first, and don't over-tighten.
5. Hinge the lid to the back of the box. Put the frame somewhere sunny and sheltered, with the low side facing south.

Tips

• Hardening off: lid open by day, closed at night, for 1-2 weeks before planting out.
• Prop the lid open with a stick on sunny days - it gets hot inside fast.

Or buy one ready made

Rather buy one? Ready-made cold frames cost about £35-80.

Thompson & Morgan · Suttons · B&Q · Wickes · Amazon

Good for growing

• Salad leaves
• Peas
• Spring onions
• Courgettes
• Swiss chard
• Beetroot
• Runner beans
• French beans
• Cherry tomatoes
• Big tomatoes
• Butternut squash
• Summer squash