To protect our peas, beans, broad beans and corn from birds, we have to net the beds. We have started using supports made from lengths of polypipe slipped over the ends of metal star stakes, or strong wooden stakes. These arches can be left in position to provide support for netting or shade cloth, as required. Shadecloth will also provide some protection from frost.
Stakes 1.8 metres (6′) in length are suitable for beds that may contain climbing plants or corn. Star stakes measuring 2.25 metres (7′ 6″) can be used for small trees or larger covered areas. For star stakes you will need (2″) 51 mm *** diameter polypipe. Wooden stakes can be used when only (1 1/2″) 38 mm polypipe is available. A semicircular arch is reasonably strong, and this is the easiest to produce for smaller areas.
*** Please Note: Flexible polypipe is still sold in imperial measurements of (1 1/2″) and (2″). Polypipe sold as 50mm diameter is high pressure pipe. It is thicker and less flexible.
This structure over our pea and bean bed was made from 1.8 m. wooden stakes embedded in soil to 30 cm, which is as far as they would go in our soil. This resulted in 1.5 m. of the stakes left exposed. The stakes were positioned on each side of the bed, 1.5 m. apart, with approximately 1.5 m. – 1.8 m. between arches. We used the taller arches here to allow the remaining popcorn cobs to complete drying on the plants. This spacing provided arches with a height of approximately 2.2 m. The structure was erected very quickly and is easy to move if necessary.
To get an idea of the size of the arch canopy you will produce, measure the width of the bed, and divide the measurement by two. Add this measurement to the height of the stakes above the ground. For example, if you are using 1.8 m. stakes, buried 30 cm, you will have 150 cm of stake exposed. If your bed is 1.2 m. wide, half this measurement is 60 cm. Add the two together and you have 210 cm, or 2.1 m. – about 30 cm lower than the average ceiling. If you need a taller arch, use longer stakes.
To calculate the amount of polypipe you will need for each arch, multiply half the width of the bed by 3.1428 (or “pi” if you have a calculator with pi), then ADD 90 cm to allow at least 45 cm to slip over the top of each stake. For a bed 1.2 m. wide, 60 cm x 3.1428 = 188.5 cm plus 90 cm = 278.5 cm. Rounding it off, each length of polypipe would be cut to 280 cm or 2.8 m.
This is an example of a more permanent structure across a series of beds. It is approximately 6 metres wide. The arches are quite flattened and require support in the centre of the polypipe lengths. The gardener has used a strip of flat steel along the centre of the roof, welded to the tops of several galvanised iron pipes set in the ground.