Cold Frame

Thu, 02 Apr 2026 00:00:00 +0000

A cold frame is a bottomless, box-like structure with a transparent cover (typically glass or polycarbonate) placed directly over garden soil to warm the soil and air beneath through solar radiation and thermal mass. It extends the growing season by creating a localized microclimate several degrees warmer than ambient conditions.

Thermodynamics

Cold frames operate on simple solar principles. Sunlight passes through the transparent lid, striking the soil below. The soil absorbs this solar radiation and converts it to heat. Unlike open air, the transparent cover traps radiated heat from the soil, reducing wind chill and preventing warm air from escaping. This creates a temperature differential of 5–10°F above ambient conditions. The soil itself acts as thermal mass, absorbing heat during the day and releasing it slowly at night, buffering against temperature swings.

Row Cover

Thu, 02 Apr 2026 00:00:00 +0000

A row cover is a sheet of lightweight, spunbond polypropylene fabric (typically 0.5–1.5 oz per square yard) laid directly over growing plants or supported on low hoops. It functions as a flexible microclimate modifier — controlling temperature, excluding pests, and reducing wind stress — while allowing most sunlight and water to reach the plants below.

Material Properties

Commercial row covers are 100% polypropylene spun-bonded with UV stabilizers for durability. The fabric is permeable to air and water, allowing gas exchange and rain penetration while trapping a thin boundary layer of warm air above the plants. Light transmission varies by weight: lightweight covers (AG-15) transmit about 85–90% of incident light, while heavier grades (AG-50) transmit around 50%.

SeasonExtension on emsenn.net

Cold Frame

Thermodynamics

Row Cover

Material Properties