Cold Frame vs. Hoop House: Season Extension Options Compared

Season extension structures let you grow earlier in spring and later into fall than your USDA hardiness zone would otherwise allow. The two most practical options for home gardeners -- cold frames and hoop houses -- both work through the same basic mechanism: trapping solar radiation to warm the.

Season extension structures let you grow earlier in spring and later into fall than your USDA hardiness zone would otherwise allow. The two most practical options for home gardeners — cold frames and hoop houses — both work through the same basic mechanism: trapping solar radiation to warm the air and soil inside the structure. But they differ substantially in scale, cost, ventilation demands, and how many weeks of additional growing season they reliably provide.

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How Each Structure Works

Cold Frame

A cold frame is a bottomless box with a transparent lid — typically old windows, polycarbonate panels, or clear plastic sheeting on a frame of lumber, concrete block, or brick. Per Penn State Extension, the standard size for a single sash is 3x6 feet (matching a standard storm window). The frame typically sits 12–18 inches high in the back, 8–12 inches in the front, angled to maximize solar gain.

Cold frames require no heating. The solar gain from the transparent lid, combined with the insulating mass of the soil inside, keeps interior temperatures 10–20°F above ambient nighttime temperatures on calm, clear nights. Per Cornell Cooperative Extension, this margin allows cold-hardy crops (spinach, mâche, kale, carrots) to survive nighttime temperatures down to 10°F in a well-managed cold frame.

Hoop House (Low Tunnel or High Tunnel)

Hoop houses are arched structures covered with polyethylene film or floating row cover. They come in two practical sizes for home gardens:

Low tunnels: 18–36 inches high; wire or fiberglass hoops spaced 2–3 feet apart; covered with floating row cover or clear poly. Stand-in work is not possible. Per UMN Extension, low tunnels provide 4–8°F of frost protection and are the cheapest season extension structure per square foot.

High tunnels: 6–14 feet high; Gothic arch or Quonset profile; covered with single or double-layer greenhouse poly. You can stand, walk, and work inside. Per Cornell Cooperative Extension, high tunnels in zone 5–6 provide 2–3 USDA zone equivalents of warming, enabling year-round salad green production when combined with floating row cover inside the tunnel.

For this comparison, "hoop house" refers to a high tunnel that allows working inside — the more significant investment and the more useful comparison point.