A cold frame is a small bottomless box with a clear top that protects salad crops, brassica seedlings and cool-season herbs through winter. They cost a fraction of a greenhouse, take up no headroom, and let you eat fresh-cut lettuce in July. The right cold frame is sturdy enough to last a decade, wide enough for a real harvest, and has a self-venting lid for the warm sunny days.
Our team’s top picks
Juwel Easy Fix 100 Cold Frame
- Twin-wall polycarbonate
- Aluminium frame
- Auto-vent included
- Solid German build
Outsunny Wooden Cold Frame
- Fir wood frame
- Polycarbonate panels
- Adjustable lid
- Honest mid-range value
Gabriel Ash Cedar Cold Frame
- Lifetime cedar build
- Glazed glass lid
- British craftsmanship
- Heirloom piece
Bio Star 1500 Cold Frame
- 1.5 m tall back wall
- Suits taller winter crops
- Aluminium frame
- Roof opens fully
Bayliss MK7 Auto Vent + Cold Frame Combo
- Wax-piston auto opener
- Triggers at 21C
- No power needed
- Brilliant for absent gardeners
What to look for in a cold frame for winter lettuce
- Twin-wall polycarbonate insulates better than glass for the same weight.
- A self-venting lid (with a temperature-triggered piston) prevents cooking the crop on warm days.
- Cedar or polycarbonate frames last; pine frames rot fast against damp soil.
- Width matters: 90 cm depth from front to back is the practical sweet spot for working from one side.
- Position against a south-facing wall (north-facing in the southern hemisphere) for the warmest microclimate.
Frequently asked questions
How cold can a cold frame protect against?
A double-glazed cold frame holds 5-7C above outside ambient. So in zone 7-9 climates (most of southern Australia and the southern US), winter lettuce, spinach, mache and Asian greens grow happily.
Do I need to vent the cold frame?
Yes — every sunny winter day. An auto-vent opener saves the crop on warm days when you forget. Without venting, winter lettuce can cook even with 5C outside air.
What can I grow in a cold frame in winter?
Lettuce (oak-leaf, romaine, butterhead), spinach, mache (corn salad), winter rocket, mizuna, mustard greens, parsley, chives, baby brassicas. Anything cool-season grows happily.
Cold frame or low tunnel?
Cold frame for permanent installations, easier daily access and longer life. Low tunnel (hoops + plastic) for temporary frost protection over a row crop, cheaper but less robust.
Bottom line
If you only take one thing from this guide, it is that quality matters more than spec on paper. The picks above have been chosen because our team uses them or trusts them — not because they are the most expensive or have the flashiest marketing. Buy once, garden often.
