If you are planning on saving your own vegetable seeds from a particular vegetable variety, a problem often encountered is the risk of cross pollination. This occurs when pollen from one variety is carried by insects or wind to the flower of a different variety and the results in the seeds being a combination of the genetic make-up of both varieties. To reduce this risk and keep your variety pure, you can make an isolation cage which will stop insects, but not the wind, from transferring any pollen to the vegetable variety you are isolating for seed saving.
To make a simple isolation cage, you need some cheap nylon fly-screen 5 times as long as it is wide, 4 canes or thin stakes, and some string and garden wire. Alternatively, you can use old net curtains, or other netting small enough to exclude insects. A piece of screen of netting1m by 5m will give a cage large enough to cover 3 or 4 plants. Cut a square piece of screen 1 metre by 1metre to make the top of the cage, and then fold the remaining strip of fly-screen round and sew its ends together. The resulting band will be the sides of the cage. Then sew the top to the sides, making a cube of flyscreen with the bottom missing.
To put up the cage over your plants, hammer the four canes into the ground in a square a little smaller than the cage top, so that they stick up a little less than the height of the cage. Twist a short piece of wire tightly round the top of each cane, and then run string in a square around the tops of the canes, supported by the wires to stop it slipping. Run a second piece of string around the stakes lower down to stop the sides of the cage blowing in against the plants. Then slip the cage over your plants, and weigh it down with earth or rocks.
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