A backyard greenhouse kit costs anywhere from $120 for a plastic tunnel to $3,300 for a cedar greenhouse with a fan and power port. Here is what to check, in order. Every model we mention is in our greenhouse table.
1. PE film or hard panels
- Pop-up and tunnel greenhouses have a steel frame with a PE plastic cover. They cost $1 to $3 per square foot and go up in an hour. UV breaks the film down, so expect a new cover every two to four seasons. They suit season extension: an early start in spring, a longer harvest in fall.
- Polycarbonate greenhouses have hard panels on an aluminum frame. They cost $4 to $10 per square foot, take a weekend to build and last ten years or more. They hold heat better and stand up to hail and wind.
- Wood and cedar greenhouses pair polycarbonate with a wood frame. They look like garden furniture and cost the most.
2. Panel thickness
Most hard-panel kits use 4 mm polycarbonate. Twin-wall (or double-wall) panels trap a layer of air, so they insulate better and spread the light evenly, which most plants like. Clear single sheets let in the most light but get hot in summer. A few kits (HOWE 8x8, Yardenaler 8x12) use 6 mm, which holds heat noticeably better on cold nights.
3. Size: buy bigger than you think
Almost every greenhouse owner wishes they had bought a bigger one. A 6x8 holds a bench on each side and room to stand. An 8x12 lets you grow tomatoes along one wall and keep seed trays on the other. Check the side wall height too: a 7 ft peak with 5 ft walls means you stoop along the edges.
4. Wind and snow ratings
Few listings publish them. The Palram - Canopia Mythos and HOWE 8x8 state 56 mph and 15.4 lb per sq ft. The HOWE 10x18 states 70 mph and 30 psf, and the Backyard Discovery cedar models state 100 mph and 30 inches of snow. If you live in snow country, pick a model with a stated snow load and brush heavy snow off the roof anyway.
5. The base
A hard-panel greenhouse needs a level, square base: a concrete slab, pavers, or a timber frame on gravel. An uneven base twists the frame, and then panels pop out in the first storm. Bolt the frame down at every corner. A pop-up or tunnel sits on soil, but stake every leg and bury the skirt flaps.
6. Venting
A closed greenhouse passes 100°F on a sunny spring day. Look for roof vents (four on the HOWE 10x18 and AMERLIFE 8x12), roll-up windows on tunnels, or an exhaust fan (the Backyard Discovery models). An automatic vent opener costs about $30 and saves plants while you are at work.
7. Warranty
Palram - Canopia and Backyard Discovery give 5 years. EAGLE PEAK gives 1 year. Most other brands state no warranty term at all, so check every part when the boxes arrive and keep the packaging until the build is done.
Next step
Compare the models side by side in the greenhouse table. Want shade instead of growing space? See the hardtop gazebo comparison.