A simple plastic tunnel like this can serve as a cold frame to grow salad greens all winter long, to grow out tomatoes and other tender plants, to extend the season for an early Spring start or a late Fall harvest, or even as a screen house to keep birds off of your strawberries or vine borer moths off of your squashes. You can also use one of these to dry out water logged beds and warm up the soil so that you can begin planting in early Spring. These devices are so useful, cheap, easy, and quick to build that everyone should have at least one – it’s almost as good as having your own polytunnel greenhouse.
- 5-5′ lengths of 3/4″ (inside diameter) polyethylene water pipe
- 10 – 1/2″ x 1/2″ x 14″ wooden stakes
- 1 – 12′ x 6′ x 4 mil clear plastic sheet
- 4 – 1/2″ x 1 1/2″ x 8′ wood strips
- staples and nails.
As usual you can (and should) substitute materials that you have available on hand. You can use anything for stakes that are strong enough to drive into the ground and will slip inside of the rib pipes. You can use a broom stick, piece of pipe or any long thin objects for the poles, and you can fasten the plastic skin to the poles with duct tape instead of staples. Clearly almost any kind of bendable pipe can be used for the ribs, but here’s a tip – contractors or plumbers are likely to have a scrap collection of one kind of plastic pipe or another that comes in coils that they will either give away or sell incredibly cheap – just ask. In the worst case, you can usually buy cut lengths at the home improvement or hardware store.
Start by cutting your parts to size – this tunnel will cover an area that is from about 2 – 3 feet wide and the black pipe for the ribs are 5′ long, and the plastic is about a foot and a half wider – you can roll up any excess plastic on the poles so it is better for it to be too wide than too narrow. In this case I made the poles shorter than the plastic so that the excess could be used to close up the ends, but you could also make the poles the same length as the plastic and use rectangles of plywood or other sheet lumber to close up the ends. Use your imagination.
Once you have your parts cut to size fasten the poles to each long edge of the plastic sheet. I used staples to do this, and then rolled the plastic around one piece of wood and fastened another strip to it so that the plastic is sandwiched between the wood pieces. If you are just using tape, then you will want to wrap the plastic around the pole and tape the plastic sheet back to itself forming a tube with the pole inside – tip: construction tape (duct or housewrap tape) sticks very well to plastic, and not very well to wood – don’t try to tape to the wood other than as a temporary measure.
Once you have that done, roll the plastic up around one of the staves until you are ready to deploy it.
In the garden, simply drive the stakes into the ground where you want them, and slip the pipes for the ribs over them. Since my ribs are made out of coiled pipe they already have the right shape, if you used straight sections of pipe you might need to use something more robust than 1/2″ wooden stakes to hold against the tension of the polytunnel ribs.
Now just roll your plastic out over the ribs and there you have it. If you experience a lot of wind you might need to weight down the plastic a bit, but under normal conditions the wooden pole will probably do the trick. When you need to get into the pollytunnel you just lift a pole and lay it over the top – almost as easy as a regular cold frame, but a lot easier to build or move.
Now would be a good time to build one!