A greenhouse brings a whole new dimension to gardening. It’s the perfect place to grow strong, healthy new plants from seed and cuttings, and to overwinter tender plants that can’t tolerate frost, excess rain and strong winds.
A greenhouse also extends your growing season – by up to three to four weeks in both spring and autumn. And there’s nothing more soothing than the sound of torrential rain drumming on the glass while you’re warm and dry inside!
In a small garden, space for a greenhouse is often restricted. Ideally they need to be positioned where they’ll get plenty of sunlight without shading by surrounding trees or houses. It’s also important to work out what you’re going to do with it: a small one is fine if you’re only going to use it to overwinter a few plants, sow a limited number of seeds in spring and grow a couple of tomato plants in summer. Other-wise, go for the biggest you can afford and accommodate, with sufficient space to add staging and shelv-ing or a potting bench. Lots of people buy a tiny greenhouse, get bitten by the greenhouse gardening bug and then find it’s too small. The reverse is also true: having a large greenhouse full of plants that all need regular attention can become stressful.
Also consider height – especially if you’re tall! The taller it is at the eaves – ideally, at least 1.5-1.8m (5-6ft) high – the better the light transmission inside.
The materials used affect not only the cost and build quality, but also aesthetics. Wood looks attractive and is a great choice for small gardens where it’s on show the whole time. Yet wood needs maintenance every couple of years or so to keep it looking good and prevent rotting. Western red cedar needs the least maintenance. Wood also retains heat better than metal structures, but the broad glazing frames do reduce internal light levels slightly.
Aluminium greenhouses are cheaper, need little maintenance, and have a certain utilitarian appeal. Many manufactures offer a choice of coloured powder coatings to improve aethetics. They don’t hold heat as well as wood, but the thin glazing bars allow excellent light transmission. The extruded channels within the frame provide potential for adding shelves, securing bubblewrap or glazing insulation and summer shading panels.
Plastic resin frames are often used with polycarbonate glazing panels. They look attractive, are cheaper than aluminium, maintenance-free, lightweight and don’t allow as much heat to escape.
Galvanised steel greenhouses are heavier than aluminium, so more robust and a good choice in windy gardens, but are more susceptible to rusting.
Glass panes are heavy, adding weight and stability, but are prone to breaking when hit by stray objects. They have good light transmission, but lose heat easily. Toughened glass is usually a better choice than standard horticultural glass.
Polycarbonate panels are lighter and won’t break or shatter. Twin-walled polycarbonate retains more heat. Styrene and other rigid plastic glazing are further choices. Just remember that plastics do deterio-rate in time when exposed to UV.
Don’t overlook ventilation – it’s essential in summer to reduce overheating, while opening vents in winter helps reduce condensation and prevents the build-up of grey mould. Roof vents are the most useful, ideal-ly on both sides of the ridge. Side, or louvred, vents help regulate air flow, used in conjunction with roof vents.