Aubergine flowers are mainly self- pollinated, but can be crossed by insects. So if you are planning to save seed, you should only grow one variety. Aim for 6 to 8 plants each year to maintain a variety long term. For 100% isolation you need 50 feet between your seed plants and any other aubergines. If you are growing them in a greenhouse you should be able to get away with a somewhat smaller distance.

To get ripe seeds let the fruits mature well past eating stage. Purple/black fruits turn a muddy purple-brown colour, green/white fruits turn yellowish. Mark 1 or 2 early good fruits on each plant to leave for seed and then pick and eat later fruits.

To remove the seed, cut into quarters lengthwise, avoiding the core, and pull apart. The hard brown seeds should be obvious. Put the quarters into a bowl of tepid water, and rub the seeds out with your fingers. You may need to pull them apart to get all of the seeds. Add more water, stir thoroughly, & wait a few minutes. Good seeds will sink to the bottom, leaving debris and poor quality seeds on the surface. Pour the debris off gently through a sieve, then refill with water and repeat a couple more times.

Eventually you will be left with good seeds in plain water. Empty into a clean sieve, shake to remove as much water as possible, and then tip on to a plate and spread out well. Put to dry somewhere warm but not hot, and mix occasionally to make sure that they dry evenly and don't stick together. Aubergine seeds will keep up to 7 years if dried thoroughly & stored in a cool dark place. More information can be found on seed drying under our section ‘Seed Cleaning and Drying’ on our website.

Making an isolation cage

To make a simple isolation cage ideal for peppers or aubergines, you need some cheap nylon fly-screen 5 times as long as it is wide, four 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 1m by 5m will give a cage large enough to cover 3 or 4 plants.

Cut a square piece of screen 1m x 1m 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 fly-screen 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.