Greenhouses

A greenhouse buys a Canadian gardener several weeks at each end of the season: seedlings start in March instead of May, and tomatoes keep ripening after the first cold nights. Our greenhouses run from a mini shelf unit to 12' x 24' heavy-duty walk-ins. The brands are ShelterLogic, Miracle-Gro and Sojag.

Most backyard greenhouses here are a powder-coated steel frame under a UV-treated cover, which is why they cost a fraction of a glass house and can be taken down if you move. Most models use a steel frame; a few use aluminum. Choose the size by what you grow: a mini unit holds trays of seedlings, a 6 x 8 ft walk-in holds a bench and a row of pots, and the 12 x 20 ft and larger frames are for serious season extension.

Two things decide whether a greenhouse is pleasant to work in: ventilation and anchoring. On a sunny April afternoon a closed greenhouse runs well above the outside air temperature, so open the door and the side vents by mid-morning and close them before dusk — most of the walk-in frames here have a zippered door and roll-up vent panels for exactly that. The covers are UV-treated polyethylene rather than glass, which is what keeps both the price and the weight down. They last longest if you brush snow and leaves off instead of letting them sit, keep the frame free of sharp burrs, and store the cover dry if you take it down for winter.

Which greenhouse size?

Type	Typical footprint	What it holds	Notes
Mini / shelf	2' x 1-1/2' to 4' x 4'	Seed trays and small pots on stacked shelves	Sits against a wall or on a balcony; the cheapest way to start seeds early
Compact walk-in	4' x 6' to 6' x 8'	A potting bench and one row of grow bags	Fits most suburban yards; anchor it, an empty frame is light
Backyard walk-in	10' x 10' to 10' x 20'	Two benches with a path between them	The usual choice for year-round vegetable growing
Heavy duty	12' x 20' to 12' x 24'	Rows of beds or a small nursery	Round or peak roof; peak sheds snow better

Greenhouse FAQ

Can a greenhouse stay up through a Canadian winter?

A covered-frame greenhouse is built for the growing season, not for carrying snow. Unless the manufacturer states a snow rating for that model, take the cover off or clear it after every snowfall — the weight of wet snow on a wide span is what collapses frames. A peak roof sheds snow better than a round one.

Is a greenhouse warm enough to grow through winter?

Not on its own. An unheated greenhouse in Canada extends the season by roughly a month at each end and protects against frost and wind; it does not replace heat. For winter growing you need a heat source and, in practice, supplemental light.

How do I anchor a greenhouse?

Every model ships with anchors, and you should use them: an empty frame under a cover is very light and a gust will move it. On soil use the supplied augers or stakes, on gravel use longer ground anchors, and on a deck or concrete bolt the base rail down.

Where should I put it?

Six hours of direct sun, out of the prevailing wind, with the long side facing south where you can. Keep it clear of the drip line of trees — falling branches tear covers — and leave room to open the door fully.

What sizes do you carry?

Sizes in the range: 2' x 1-1/2', 4' x 4', 4' x 6', 6' x 6', 6' x 8', 7' x 8', 10' x 10', 10' x 20', 12' x 20', 12' x 24' — from mini shelf units to heavy-duty 12' x 24' frames.

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