Cold Frames

How to choose the best cold frame

Still not sure which option is right for your garden? Here are a few common questions people ask about cold frames, and their answers.

What are a cold frame’s main uses?

A cold frame has three main purposes:

• Hardening off young plants – the process of gradually introducing indoor-sown plants to outdoor conditions.
• Overwintering established but tender plants like pelargoniums, protecting them from the worst of the frost.
• Finally, you can use it as a mini greenhouse to sow hardy crops like winter lettuce or carrots earlier in spring and later into autumn.

How do I harden off plants in a cold frame?

Hardening off plants in a cold frame is a simple process, taken over a couple weeks. The exact timing will depend on where in the UK you are (those in the south tend to start earlier), and it should be after all risk of frost has passed. Place your young plants inside the cold frame and keep the lid closed for the first few days.

For the next few days, open the lid during the daytime and close it at night. For the final few days, leave the lid open day and night. After a fortnight or so, your plants will be fully acclimatised and ready for planting in their final positions. Check your plants’ hardiness before you decide when to set them out to harden off.

What's the difference between a cold frame and a lean-to mini greenhouse?

A traditional cold frame is a low-to-the-ground box with a sloping lid, designed primarily for hardening off and protecting small plants. A lean-to mini greenhouse is taller and stands against a wall. Its extra height and shelving make it ideal for growing taller plants like tomatoes or peppers, as well as for storing and protecting plants on a patio or balcony where space is limited.

Should I choose a wooden or an aluminium cold frame?

This choice is largely down to how you want it to look, and how much maintenance you’re prepared to do. Wooden cold frames offer a classic, traditional look and provide excellent natural insulation. They may require occasional treatment to protect the wood from the elements. Aluminium cold frames are very lightweight, easy to move, and require virtually no maintenance, offering a modern and durable alternative.