Choosing and siting a greenhouse

Greenhouses come in aluminium or timber. Aluminium is cheaper, lighter, and lasts decades without maintenance. Timber looks better, insulates slightly more, and rots if you forget to treat it every three years. Both work. The frame matters less than the glass: always choose toughened or horticultural glass over polycarbonate if you can. Glass transmits more light, does not yellow with age, and allows you to see your plants clearly from outside.

Size is where most people underbuy. A 6×8-foot greenhouse feels generous until you fill one side with tomatoes and realise there is no room for seedlings, cuttings, and overwintering pots. If your budget allows, go to 8×10 feet or larger. You will use every inch. Smaller than 6×6 feet and you have built an expensive coldframe.

Siting is critical. The greenhouse wants full sun from March to September, which usually means an east-west ridge orientation so the long sides face south. Avoid placing it under trees — shade is one problem, falling branches and sticky aphid honeydew are worse. It should be close enough to the house that you visit it daily in winter without dread, but far enough that you are not staring at condensation-streaked glass from your kitchen window. Level ground is non-negotiable; a greenhouse on a slope will twist and leak.

Foundations depend on size. Smaller greenhouses can sit on a timber frame sunk into gravel. Anything over 8×10 feet wants a proper concrete footing or pier-and-beam base. The investment is worth it. A well-founded greenhouse will outlast you.