Greenhouses · Season extension · Frost strategy
Your last frost date is a suggestion.
Defy Frost reviews the greenhouse kits, high tunnels, and cold-weather gear that keep things growing when the calendar says stop. Owner data, BTU math, snow-load facts. Winter is a solvable problem.
Built on numbers, not brochures
Three readings from our reviews. The kind of figure the manufacturers leave out and the listicles never compute.
- Riga price per sq ft
- $96$56
- The smallest Riga 2s costs $96 a square foot; the mid-size Riga 5 lands at $56. Buy by the foot, not the sticker.
- Permit-exempt threshold
- 120sq ft
- Under the IRC, a detached accessory structure is permit-exempt at 120 square feet or less. A 10×12 greenhouse sits exactly on the line.
- Base cost swing, 10×12
- $800
- A gravel pad runs about $150; a pro-poured slab about $960. For a freeze climate, the cheaper base is also the better-performing one.
Know your enemy
How hard is your winter?
The right structure depends entirely on what you're up against. We sort the fight by zone, not by price. Find yours.
- Z8+ Mild winters Frost visits, it doesn't move in. A frost blanket, a cold frame, or an unheated hobby kit covers most of the fight here. Season-extension guide
- Z5–7 Real winters Greenhouse country. Twin-wall polycarbonate, honest heater math in BTUs, and the kits that hold the line through a hard freeze. Heater math, in BTUs
- Z3–4 Brutal winters Snow-load ratings stop being fine print. The Riga class, glass orangeries built like ships, and engineering that earns its price. Snow-load ratings
From the field
All articles
Best 4-Season Greenhouse Kits for Cold-Climate Growing
Greenhouse kits that handle cold winters. Glazing thickness, snow load ratings, and the structural features that determine year-round growing performance.
Best Budget Greenhouse Kits Under $1,000: What to Buy
What a greenhouse budget under $1,000 actually buys. The honest comparison between fabric pop-ups, polycarbonate starter kits, and hoop houses.
Best Greenhouse Kits: Ranked by Total Cost of Ownership
Greenhouse kits compared by total cost of ownership. Frame quality, glazing thickness, and the base costs most listings bury determine the real price.
Bootstrap Farmer High Tunnel Review: 16-Gauge Steel Kits
Bootstrap Farmer high tunnel kits reviewed: USA steel from $768, the Essential-vs-All-Metal fork, NRCS cost-sharing, and when a tunnel beats a kit greenhouse.
Canopia Grand Gardener Greenhouse Review: Specs and Verdict
Barn-shaped polycarbonate kit with resin frame and 4mm diffused twin-wall roof panels. Four sizes. US retail stock not confirmed as of June 2026.
Canopia Glory vs Hybrid Greenhouse: Which One to Buy
The Glory uses 10mm twin-wall throughout; the Hybrid mixes 4mm twin-wall roof with single-wall clear walls. Same brand, very different price points.
The questions every grower asks first.
Do greenhouses work in winter?
Yes, with the right expectations. An unheated greenhouse buys roughly one to two USDA zones of protection: cold-hardy crops keep producing while tomatoes still die. Add modest heat and insulation and the growing season simply stops ending. The difference between disappointment and a January salad is matching the structure to your zone.
How much warmer is a greenhouse than outside?
On a sunny winter day, 20 to 40 degrees warmer inside is normal. On a cloudy night, an unheated greenhouse holds only 2 to 8 degrees over the outside air, which is why night strategy, thermal mass, row covers inside, or a small heater, decides what survives. We publish the math per structure type.
Do I need a foundation for a greenhouse kit?
Small kits under about 50 square feet can sit on a leveled, anchored timber base. Bigger or more permanent structures want a proper perimeter foundation, and snow country makes that non-negotiable. Anchoring matters more than people think: an unanchored greenhouse is a kite with panels.
When should I cover plants for frost?
When the forecast touches 36 degrees, cover that evening: official frost readings happen at five feet, and ground level runs colder. Covers go on before sunset to trap soil heat and come off in the morning. A frost blanket buys 4 to 8 degrees; an old bedsheet buys 2 to 4.
Owner reports in. Numbers computed. No guesswork.
Hundreds of verified owner reviews per kit, heating costs in real BTUs and dollars, snow-load ratings from the manufacturers' own sheets. When something is unverified, we say so.