A cold frame is a low box with a clear lid. It catches the sun, keeps off wind and rain and stays a few degrees warmer than the open garden. You do not get much space, but you get a lot of use from it, from early sowings in March to salad leaves in October.
What you use a cold frame for
- Hardening off: plants raised indoors or in a heated greenhouse need to get used to outdoor conditions before planting out. Put them in the cold frame and open the lid a little more each day for one to two weeks.
- Early sowings: lettuce, radish, spring onions and peas start earlier under a lid.
- Late crops: salad leaves and herbs last longer into autumn.
- Overwintering: hardy seedlings and cuttings get through winter better out of the wet.
Tender plants such as tomatoes and courgettes should only go outside unprotected once the risk of frost has passed, which in much of the UK means late May or early June, and later in the north and in frost pockets. A cold frame fills that gap.
What to look for
- A lid that props open at several heights. On a sunny day a closed cold frame overheats fast.
- A polycarbonate lid rather than thin plastic, as it lasts longer and holds heat better.
- Enough height for the plants you want to harden off. Tomato plants in pots need more room than seed trays.
- Solid sides of timber keep wind out better than open frames.
Two examples from our list
The Christow Raised Bed Cold Frame (100 x 65 x 40 cm) is a timber raised bed with a lid, so you can grow straight in it. The Outsunny Wooden Cold Frame (100 x 50 x 36 cm) is a smaller timber frame. Scores and specs are on their product pages below. Compare all cold frames.
Tips
- Put the cold frame against a sunny wall or fence. The wall gives back warmth at night.
- Open the lid on any sunny day, even in winter.
- On frosty nights, put an old blanket or bubble wrap over the lid.
- A heated propagator indoors plus a cold frame outside covers most of what a beginner needs a greenhouse for.
