How to Build and Use a Cold Frame for Year-Round Gardening

A cold frame is a bottomless box with a transparent lid — a passive solar heater that lets you garden months earlier and later. Unlike a hotbed (which uses electric cables or manure), a cold frame runs on sunshine alone. Simple, cheap, and incredibly useful.

Design Basics

• Orientation: Face south/southeast for max sun.
• Wind protection: Place against a north wall, fence, or hedge.
• Insulation: Sink into ground 6–12" or berm soil around sides.
• Lid: Sloped southward. Glass (traditional) or twin-wall polycarbonate (lighter, safer).
• Size: 4–5 ft wide (reach center), any length.

Construction Options

• Wood sides (cedar, locust, or copper-naphthenate treated — not creosote/penta).
• Concrete blocks or straw bales (temporary).
• Kits (easy, often include vents).
• Dutch lights (portable, large).

Using It Through the Seasons

• Late winter: Start cool crops (spinach, lettuce, brassicas). Vent when >45°F.
• Spring: Harden off seedlings — gradually increase vent time.
• Summer: Shade cloth + vent = heat-tolerant starts.
• Fall/winter: Grow carrots, kale, mache, claytonia. Insulate with blankets/burlap on freezing nights.
• Root cellar mode: Dig 12–18" deep, layer straw, store root crops (carrots, beets, turnips) under lid + tarp.

Ventilation is the #1 skill — too hot kills faster than too cold.