Simple Cold Frame
A bottomless box with a sloped glass or polycarbonate lid that captures solar heat and protects tender plants from frost.
Estimated cost
$40 – $80
Estimated time
1.5 – 2 hours
Lifespan
5–8 years
Soil needed
Fills the box — about 8 cubic feet
Weight empty
30–50 lbs
Weight full
250–350 lbs with soil and lid
Best for
Overwintering greens, hardening off seedlings, starting cool-season crops early
Placement
Face the sloped lid south. Nestle against a wall or hedge for wind protection. Prop the lid open on sunny days.
Boards to Buy
| Boards to Buy | Quantity | What You Use Them For |
|---|---|---|
| 1×8 cedar or rot-resistant boards, 8 ft | 3 | Front, back, and sides |
| 1×2 cedar strips | 2 | Lid frame |
| Polycarbonate sheet or old window, 4 ft × 2 ft | 1 | Lid glazing |
| Exterior hinges | 2 | Attach lid to box |
| 2.5-inch exterior screws | 1 lb box | Assembly |
- ·Optional: automatic vent opener
- ·Optional: stick or prop for manual venting
Steps
- 1Cut the back board 24 inches long and the front board 16 inches long.
- 2Cut two side boards that slope from 24 inches in back to 16 inches in front.
- 3Screw the box together so the front, back, and sides form a rectangle.
- 4Build a matching lid frame from 1×2 strips.
- 5Attach the polycarbonate or window to the lid frame with screws and washers.
- 6Hinge the lid to the back of the box.
- 7Set the cold frame on prepared soil or over a raised bed.
- 8Prop the lid open 2–6 inches on sunny days to keep from overheating.
- 9Plant cold-hardy greens in late summer for winter harvest, or use it to harden off seedlings in spring.
Tools needed
- ·Circular saw or miter saw
- ·Cordless drill / driver
- ·Tape measure
- ·Speed square
- ·Safety glasses
Common mistakes to avoid
- ·Building a flat lid — rain pools and it overheats faster
- ·No venting — plants cook on sunny days even in winter
- ·Using single-pane glass in a windy spot
- ·Placing it in deep shade or where water pools
Maintenance tips
Prop the lid open on sunny days. Replace weatherstripping if it rots. Empty and store the lid before heavy snow if it cannot bear weight.
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