Where to put it

Glasshouses (greenhouses) and polytunnels should be sited in a sheltered area to keep them as warm as possible, but somewhere where plenty of light is available. When selecting the site consider where shadows will be cast by nearby structures (eg trees and houses) and keep in mind that shadows will be longer in the winter, when the sun isn’t as high.

Shelter

Shelter can be provided by distant trees acting as a windbreak, or closer hedging or open weave fencing. They don’t need to be very close to the structure, in fact you don’t want them too close as they will block out sunlight. A good general guide is that the shelter should be 4 times it’s height away from the structure, to give the best shelter without blocking out too much light. So a 1m high hedge should be 4m away, a 2m hedge should be 8m away, and so on. On the northern side of the structure you can afford the shelter to be much closer, if necessary, as less light will enter from this side anyway.

Orientation

There is much debate about which way to orientate glasshouses and polytunnels. A good rule of thumb is to work out what you’re going to use it for most of all. If you’re going to be growing crops in it over the summer then a north-south orientation (along the length of the structure) would be best to get the most from the summer sun. If you’ll be using it more to raise plants in the spring or to overwinter tender plants, then an east-west orientation along the longer axis of the structure will ensure that light is provided for most of the day. If you’re not sure or intending to use it for a wide range of purposes then east-west is generally the best way to go.

If you have a lean-to glasshouse then erect it against an east or west facing wall so you get sun for part, but not all, of the day to prevent it overheating in summer.

Access and amenities

When positioning your structure you also need to consider access and amenities. Access is particularly important in winter months when you may need to get to it in the dark, so make sure there’s a clear path and that it’s not too far away. Easy access is particularly important if anyone using the structure is elderly, infirm or in a wheelchair. You will need to have a water source nearby the structure (such as a water butt, though you may find a mains tap more convenient) and you may wish to be near an electricity supply for providing heating and light (although both can be provided through other power sources).

What lies beneath

If you are intending to grow in the soil under your structure, then make sure you pick a site which has nutrient-rich soil with a good structure. The ground will also need to be level for a greenhouse to sit on (foundations will be required for large structures). You can ‘get away’ with a bit of a slope for polytunnels, but not a steep gradient.

The surrounding area

Finally, keep in mind who else uses the garden or may be passing nearby. Children playing, pets running around and traffic are all hazards which your glasshouse or polytunnel could do with being protected from. If you have children or pets you might want to fence off the structure, or put it well out of their way, to prevent damage to it or them!

If you are intending to put up a sizeable glasshouse or polytunnel you should check with your local planning authority before you do so, in case you need to obtain permission first.