Building a Polytunnel

What is a Polytunnel?

Propagating your own seedlings from seeds and growing small plants at any time of year is very easy with this basic inexpensive polytunnel that you can build yourself in a short time from readily obtained materials.


How does a Polytunnel work?

A polytunnel can be a lightweight greenhouse of small to large (eg commercial) dimensions. If constructed with a bit of care it can be quite weather resistant, versatile and practical. It is a great way to begin to learn a fundamental gardening technique – producing your own plant seedlings cheaply.

It is a useful aid in extending the growing season, beginning in winter, in Canberra’s “cool climate”. There are many ways to construct a polytunnel. The outline presented here is for a small polytunnel suited to the Canberra region, or equivalent.


Construction phase

Firstly, chose a suitable spot which receives at least 6 to 8 hours direct sunlight per day. It should be reasonably flat, whilst avoiding pooling of water. Orientate the polytunnel so that one side is facing north.

Mark out the area where you wish to build the polytunnel eg at least 1.5m wide and 2 to 3m long. Cut some metal curtain rods or wooden dowelling rods into sections (stakes) about 20cm long – these need to fit into lengths of poly pipe or tubing (19mm diameter preferred) to form the frame of the polytunnel. The wooden dowelling stakes should be sharpened to a point or cut at an angle to enable easier driving into the ground.

Drive the metal or wooden stakes in pairs into the ground about 1m apart. Push the poly pipe onto these stakes. The poly pipe needs to be long enough (eg 2m) to form a semicircular hoop. These hoops can be cut from a longer length of poly pipe or made from shorter lengths joined with compatible joiners.

PT 01

Once the hoops are in place, about 1m apart, place garden stakes (or equivalent), about 1.5m from each end of the proposed polytunnel. Run a rope to form a “backbone” between the end stakes, attaching them to the hoops on the way – this adds some rigidity to the structure.

PT 02

Place builders film (or shade cloth if using the polytunnel in warmer weather) over the hoops, with enough material at each end to reach the ground near the end stakes, and wide enough to cover the structure with sufficient excess to allow bricks or stones to be installed along the sides to secure the film.

The film can be lifted at either end to allow passage of air to avoid overheating on sunny days and lifted along the sides to allow access. The film should be put back in place overnight. Secure the film to the hoops with ready-made clips or DIY clips made from short lengths of poly pipe, split along their length.

PT 04

The seed germination trays should be off the ground inside the polytunnel, eg sitting on bricks or inverted small pots. Fill the trays with potting mix and sow some seeds as appropriate into them.

Your polytunnel is ready to produce seedlings. Remember to open at least one end on sunny days and to water/add fertiliser as appropriate.

PT 05


What you’ll need

Materials:

  • Builders’ film (roll) – various lengths available; shade cloth for warmer weather
  • 19mm irrigation poly pipe – cut to length or join with joiners if shorter lengths (eg 1m)
  • Stakes eg short sections of curtain rods or wooden dowelling rods
  • Camping pegs/garden pegs for the ends
  • Rope
  • Bricks or stones
  • Seedling trays (at least four to start)

Tools:

  • Tin snips or large scissors
  • Mallet or hammer

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