A cold frame is the simplest mini greenhouse. A wooden box with a glass lid. Sun heats the air inside, glass retains warmth.
Construction
Back wall 40–45 cm, front 25–30 cm. The slope ensures water runoff and better sun angle. Lid — an old window or polycarbonate. Size: 1×1.5 meters is optimal.
Placement
South-facing, wind protection from the north (house wall or fence). Maximum sun — at least 6 hours direct.
Use
Spring: seedlings 4–6 weeks earlier than open ground. Fall: extend the season by 4–6 weeks. Winter: growing cold-hardy crops (spinach, lettuce, radish).
Ventilation
On sunny days it can hit 30–40°C inside — plants will cook. Prop the lid open during day, close at night. The Amish use a simple stick prop — easy and effective.