Practice

Hoop House

Also known as: high tunnel, polytunnel, unheated tunnel

A large, walk-in, unheated season-extension structure — typically a metal or PVC hoop frame covered in a single layer of greenhouse plastic, 10 to 30 feet wide, 30 to 100+ feet long. Distinguished from a greenhouse by the absence of supplemental heating or supplemental light; the warming comes entirely from passive solar gain. Provides roughly one hardiness zone of winter warming (often more in mild climates) and dramatic season extension at both ends of the year. Now standard infrastructure on small-scale market gardens worldwide.

A hoop house is what the [[cold-frame|cold frame]] becomes at human scale. Same principle — plastic, sun, trapped heat — extended into a walk-in structure that covers an entire bed-block or more.

What makes it different from a greenhouse

No supplemental heat. All warming is passive solar.
No supplemental light. Day length is what the sky provides.
Often no automatic venting. Side roll-up walls or end-wall doors are hand-operated.
Usually a single layer of plastic rather than the double-layer or rigid panels of a greenhouse.
Production is in-ground, not in pots on benches.

The result: a hoop house is much cheaper to build and run than a greenhouse, while still providing most of the season-extension benefit for cold-hardy crops.

What it actually does

A hoop house at 44° North in zone 4–5 (Coleman’s Four Season Farm in Maine is the working reference) provides:

Roughly one hardiness zone of warming — the inside of a Maine hoop house in January performs roughly like an unprotected garden in Pennsylvania.
Wind block — substantial; wind is much harder on plants than cold alone.
Rain control — production not interrupted by wet weather; foliar disease pressure reduced.
Temperature buffering — much smaller diurnal swings than open ground.

What grows in one

In winter, with no supplemental heat:

Cold-hardy greens — spinach, mâche, claytonia, tatsoi, mizuna, arugula, kale
Roots — carrots, beets, turnips (overwintered for early-spring harvest)
Alliums — leeks, scallions, sometimes onions and garlic on extended schedules

In spring (March–May), with no supplemental heat:

Major head-start window for everything that will eventually move outside
Salad and herb succession at field scale

In summer:

Heat-loving crops — tomatoes, peppers, eggplant, basil, cucumbers (with venting) — that produce earlier, longer, and with less disease than outside

In fall:

Continuation of summer crops 4–6 weeks past first frost
Early winter cold-hardy crops getting established

A note on within-tunnel layered protection

The most-productive cold-climate hoop-house operations combine two layers: the tunnel itself, plus row cover or low tunnels on the beds inside. This stacks ~15°F of warming on top of ~15°F of warming, getting Maine winter performance to approximately Virginia winter performance. Eliot Coleman’s published figures.

Cost and scale

Small home-scale hoop house (10×20 ft): ~$300–$1,500 in materials depending on whether you have pipe-bending tools and how durable a build you want
Production-scale market-garden tunnel (20×50 ft): ~$3,000–$8,000
Commercial high tunnel with engineered components, motorized venting, etc.: $10,000+

The USDA NRCS High Tunnel Initiative has cost-shared thousands of hoop houses for small farms in the U.S. since 2010.

Sources

Eliot Coleman, The Winter Harvest Handbook (Chelsea Green, 2009)
USDA NRCS High Tunnel Initiative — program documentation and cost-share guidelines
Adam Montri & Mike Hamm, Climate Change and Hoop House Production (Michigan State Extension)

Rooted in life.

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Practical

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Low Tunnel same principle, smaller scale, much lower cost

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