Where you place a new greenhouse or polytunnel can make the difference between growing success and failure, so it’s important to get it right.
Find out how to build a greenhouse.
Of course, there may only be one site for your greenhouse but if you do have a choice, it’s worth giving it the best possible position. You’ll need a spot with maximum light and sunshine, away from frost pockets and cold winds.
It may seem a shame to sacrifice a prime location or an already productive spot in your garden, but when you weigh up the increased benefits - being able to grow crops all year round, extending the growing season, raising seedlings and overwintering tender plants - it’s a sacrifice worth making.
Discover the six essentials of siting a greenhouse, below.
Don’t put your greenhouse directly under trees. They’ll cast shade, which encourages green algae to build up, blocking even more light, while falling branches and leaves can cause damage and block guttering. Honeydew from insects on the foliage of trees can make the glass or plastic sticky and dirty. Tree roots can also upset the foundations and make planting directly into the beds inside tricky.
As you’ll be visiting your greenhouse or polytunnel regularly, particularly during the summer, make sure it’s easy to get to and as near to the house as possible. Whether your visits are for damping down, daily watering, opening and shutting doors and vents, or just nipping in to pick a few tomatoes for your lunch, you want it to be close at hand.
Avoid putting your greenhouse or polytunnel on a slope. Although it is technically possible, it would make things complicated, as the staging inside needs to be horizontal. Definitely don’t site it at the base of a slope, as this is often a frost pocket where coldness lingers – which doesn’t make for successful winter growing.
If you want to grow crops all year round, it’s best to line up the ridge of the structure to run east-west, as this will maximise light during the winter. It will also help it to heat up more quickly after cold nights. If you only intend to grow summer crops, aligning the ridge north-south is preferable as it gives an equal amount of sun to each side and helps to reduce overheating on the hottest days.
Ensure there is at least 1m of space all around your structure. Not only does this make putting it up easier, but it’s useful when panes or covers need replacing, and when cleaning or simply walking past. Leaving this space will also mean that fences and other structures aren’t close enough to cast shade or hinder ventilation. With polytunnels, always allow plenty of space at the front too, as opening the door is usually the only way to ventilate it – and good air circulation inside is vital.
If you’re planning on growing in the beds inside your structure, choose a spot with decent soil, if you can, as you’ll be asking a lot from it. Poor soil can be improved by digging in organic matter, and raised beds are a good option, particularly in a polytunnel. Try to avoid stony or rocky ground, as it can make the construction process problematic.