A cold frame is a bottomless box with a salvaged window on top. No electricity. No heater. About fifteen dollars in lumber and a window someone threw away.
The glass traps solar heat and raises the temperature inside enough to start crops six weeks before last frost and keep them going six weeks past first frost. Three extra months of food from a box you can build in an afternoon.
The whole thing is four boards screwed together with the back taller than the front so the glass slopes toward the sun. The window sits on top — hinged or just resting there. The box sits directly on soil. That’s the entire build.
What grows inside one:
– Lettuce — cut-and-come-again greens starting in early March
– Spinach — stays cool enough that it won’t bolt
– Radish — ready in under a month, sow a new row every two weeks
– Kale — frost actually sweetens the flavor
– Carrots — slow but protected from freezing soil
The one thing that kills seedlings in a cold frame isn’t cold — it’s heat. On sunny days the interior climbs fast. Prop the window open with a stick when it’s warm and close it at sunset.
Four boards, one window, twenty screws. Your cold climate neighbors are still waiting for late spring.