A cold frame sits low to the ground and acts like a miniature greenhouse without artificial heat. Its transparent lid—glass or rigid plastic—traps solar warmth while the solid sides block wind. Gardeners use cold frames to harden off seedlings, extend the harvest of salad greens, or start plants earlier than open ground allows.

Construction can be as simple as old window sashes laid over a wooden box or as refined as a hinged polycarbonate top on brick walls. Ventilation is essential on sunny days; prop the lid open to prevent overheating. In winter the frame still protects hardy crops from the worst frost and snow.

Place the cold frame in a south-facing spot with good drainage. Soil inside can be ordinary garden loam or a mix of compost and grit. With careful management, a cold frame bridges the gap between indoor seed starting and full outdoor planting.

• Transparent roof traps solar heat
• Protects plants from cold and wind
• Useful for hardening seedlings
• Requires daily ventilation in sun