If building a greenhouse seems too complicated and expensive but you want to keep on growing your vegetables during the winter, there’s a solution that suits you perfectly: a tunnel.
Similar to a greenhouse but smaller, a tunnel is half-cylinder shaped and covers the ground protecting your plants from the cold. You can find complete tunnel kits on sale, but you can also build a DIY one, maybe by using materials that you already have at home. Here are a few tips.
Where to position your tunnel
The first thing you need to do is decide where you want to put your tunnel. It’s a good idea to keep it as sheltered from the wind as possible: a strong gust could blow hours of work away.
Sunlight is essential, so the orientation of your tunnel should guarantee that it’s exposed to the sun for as long as possible; the ideal position is on a north-south axis. Where your tunnel is placed in relation to other buildings and trees is also important: on one hand, they can be useful to provide shelter from the wind but, on the other hand, they can cast shade and reduce the advantages of the covering.
A tunnel is quite simply a frame, made up of lots of small arches placed in a row, covered by plastic sheeting.
The arches can be made of various materials: from ecological bamboo canes, unfortunately rigid and not very versatile, to rebars (the metal rods used as reinforcement in buildings), or the galvanize pipes used in plumbing.
To give the frame stability it’s a good idea to connect the arches together; you can use wire to do this, better still if galvanized.
The most commonly used covering material is polyethylene, it’s cheap and can be found in various sizes, however it deteriorates rapidly and doesn’t have any particular insulating properties. PVC is slightly better, at least from the point of view of durability and heat insulation, but in the course of time it tends to loose its shape. Its use also encourages the build up of humidity inside the tunnel, so watch out, and remember to make sure that the air circulates properly.
The best material to use for your covering is certainly EVA (Ethylene Vinyl Acetate). It costs more than the other two, but it lasts longer and therefore in the long run gives you valueyou’re your money.
The thickness of your sheeting is a detail not to be ignored; the best choice depends on the climate in your area: generally speaking, a thickness of 15 mm is fine in milder areas, while it’s better to choose 20 mm in colder locations.
Lastly, to fix the covering to the ground, you’ll need some pegs - the kind used for camping are fine - and some rope or, better still, elastic straps, like the ones you use to fix luggage on a roof rack.
Bear in mind that the tunnel needs to be at least one metre high and one metre wide. This size permits you to enter it easily – remember that you will need a small central path – and guarantees a minimum volume of air to heat up.
Once you’ve chosen the dimensions, you can define the size of the sheeting and the length of the arches; for the latter consider that you need to add 20 – 30 cm on each side, which will then be stuck into the ground. To bend the pipes for your frame you can use a specialized tool such as a pipe bender or, if you are using rebars, you can shape them around something circular, such as a bin.
When you fix your arches in the ground don’t leave more than one and a half metres between them, in areas where it may snow reduce this distance to maximum one metre. Connect the arches together with three rows of galvanized wire, one in the centre and one at the bottom on each side, wind them around each arch and fix the ends to the ground with pegs.
Lay the sheeting over the frame and secure it to the arches with ropes or elastic straps, which are then fixed to the ground with pegs.
Now your tunnel is ready, so just keep on growing!