How to Choose a Backyard Greenhouse

A greenhouse is one of the larger purchases most gardens will see, and most of the important decisions happen before you look at a single model. This guide walks through them in the order we would make them. We have not tested any greenhouses for this guide; it is general guidance to help you compare listings.

Start with how you will use it

Be specific about the job. Starting seeds in spring needs bench space and light. Overwintering tender plants needs protection from frost and, in colder zones, some heat. Growing tomatoes or cucumbers through summer needs headroom and a lot of ventilation. A greenhouse you can also sit in needs a wider door and room to move.

Write down what you want to grow and roughly how much bench or floor space that takes. It is common to find the first greenhouse fills up within a season, so if the site allows, size up one step rather than down.

Pick the site before the model

Most greenhouses do best with as much direct sun as possible, especially in winter when the sun is low. Look for:

Light: an open spot clear of trees and buildings to the south. In hot summer climates, some afternoon shade can help.
Level ground — or room to build a level base.
Shelter from strong wind, without being shaded by the windbreak.
Access: a firm path to the door, and water (and power, if you want heat or lighting) within reach.

If your space is tight, a lean-to or wall-mounted greenhouse uses an existing wall for support. A south- or west-facing wall also stores heat during the day and releases it at night. Check how the frame fixes to the wall and where rainwater from the roof will go.

Frame materials

Aluminum frames are light, rot-free and common. They need a secure base and anchoring.
Wood frames (often cedar) look softer in a garden and insulate a little better, but need periodic care.
Steel frames are strong and often used for larger tunnels and commercial-style structures.

Whatever the material, look at how the parts connect and what the listing says about wind and snow loads, if anything. If those figures matter where you live, ask the retailer before ordering.

Glazing

Glass (ideally toughened/tempered) gives the clearest light and lasts, but is heavier and needs a solid base.
Twin-wall polycarbonate is lighter, shatter-resistant and insulates better than single glass, with more diffused light.
Polyethylene film is low-cost and common on hoop houses and tunnels, but needs replacing every few years.

Check whether the panels are included, how they are held in place and whether replacements are available.

Ventilation matters more than most people expect

A closed greenhouse on a sunny day overheats fast. Roof vents let hot air out; side louvers or an open door let cooler air in. A common rule of thumb is to aim for vent area equal to roughly a fifth of the floor area, and automatic vent openers take the daily guesswork out. Shade cloth or shade paint helps in high summer.

The base and anchoring

The base is easy to underestimate. Depending on the greenhouse and your soil, options include a timber or steel base frame, a row of pavers or blocks, or a concrete slab or footing. Larger glass greenhouses often need a solid, level foundation. Check:

what base the manufacturer specifies or sells,
how the frame is anchored against wind,
whether the floor will be paved, gravel or soil beds.

Permits and rules

Many US towns treat larger greenhouses like sheds: there may be size limits, setbacks from property lines and, above a certain footprint, a permit requirement. HOA rules can also apply. Check with your local building department before you order — it is far easier than moving a finished greenhouse.

Before you buy: a quick checklist

The footprint and height fit the site, with room to open doors and vents.
You know what base it needs and who will build it.
The listing states the frame material, glazing type and what is included.
There is enough ventilation, or you can add it.
You have checked local permit, setback and HOA rules.
Delivery: large kits often arrive curbside on a pallet. Plan how you will move the parts.