What is a cold frame good for?
A cold frame captures sun and shelters plants from wind and frost. Gardeners use it to harden off seedlings before transplanting, grow cool-season greens late into fall, and start crops earlier in spring. It will not heat tender plants through a hard freeze unless you add insulation.
Timing depends on your frost dates and local weather. Ask your extension office for your area's average last and first frost dates and how they apply to cold-hardy crops.
If you are unsure how your frame will perform, run it for a few weeks with a thermometer and no plants. The readings will show how quickly it heats and cools in your conditions.
Where do I place it?
Face the clear lid toward the sun, which in most of the Northern Hemisphere means the south. Pick a spot with good drainage and shelter from wind, and near enough to your door that you will check it daily. A back that is higher than the front lets the lid slope so rain and snow shed and light enters at a good angle.
Avoid low spots where cold air pools and water collects. A bed beside a south-facing wall can add a little warmth.
Think about how you will reach the frame in winter. A path that is cleared of snow and a lid that you can lift with a gloved hand make it more likely you will vent it on a sunny day. A frame that is hard to reach will be forgotten.
What size and materials work?
Keep the width small enough that you can reach every plant from the front with the lid open. Common materials are untreated wood, block, straw bales and recycled windows. Make the lid light enough to lift easily and strong enough to hold snow.
If you reuse old windows, check for lead paint on the frames and for broken glass, and consider rigid plastic panels where children or animals are near. Avoid treated lumber where soil will touch food crops, and ask your extension office about current guidance.
- Lid angled toward the sun
- Reach width manageable from one side
- Tight corners to block drafts
- Lid prop or hinge that holds securely in wind
How do I prepare the soil inside?
Treat the bed like any garden bed. Loosen the soil, add compost if a soil test suggests it, and keep it moist. A test through your extension office tells you what the soil needs, and you should follow the lab's advice instead of guessing.
Rotate crops over the years to reduce disease buildup, and refresh the soil or replace the top layer if problems appear.
Drainage inside the frame matters. Soggy soil in a cold box invites rot and disease, so keep the bed loose and avoid watering late in the day. Where frost heaves the soil, check that the frame has not shifted and that the lid still seals.
How do I manage heat and cold?
The biggest risk is overheating. A closed frame in sun can climb to damaging temperatures even on a cool day, so prop the lid open when the sun is out and close it before the air cools in the afternoon. A thermometer inside tells you more than your own sense of the weather.
On cold nights, close the lid and add insulation such as a blanket or straw over the top. Remove covers in the morning, and do not leave heavy coverings on in daylight, which blocks light.
What can I grow in it?
Cool-season greens, radishes and other hardy crops do well, and seedlings of many vegetables can be hardened off in the frame. Match crops to your region and the season, and check seed packets for temperature guidance.
Water carefully. Plants in a cold frame need less water in cool weather, but they dry out fast on sunny days. Check soil moisture by hand instead of following a schedule.
Use a simple notebook to record the dates you plant, vent and harvest. Over a couple of seasons the notes will show you how far your frame can extend the season in your climate, which is information no general chart can give you.
How do I keep it going through the seasons?
Clean the lid so light gets through, and repair cracks and gaps before the cold season. In summer, remove the lid or shade it and use the space for storage or a crop that likes warmth.
Keep notes on what you planted, dates and results. After one season, you will know how your site behaves and can improve the design.
Key takeaways
- Use a cold frame to harden off seedlings and extend cool-season crops.
- Face the lid toward the sun and shelter it from wind.
- Vent early on sunny days to avoid overheating.
- Check old windows for lead paint and broken glass.
- Use your local frost dates, not a universal calendar.
Sources and further reading
Last reviewed: November 12, 2026. Written by the Homestead & Small Farm Editorial Team. See our editorial policy.