Aubergines are ready for picking when they are about 15 cm (6”) long and have stopped swelling. The skin should be bright and shiny, and have a good, rich colour. The purple varieties will have this colour right from the time when they are first formed. Test for readiness by gently pressing the fruit with your thumb. If the indentation remains, swelling has stopped and the fruit is ready for picking. Do not leave fully ripe fruit on the plant, as the gloss on the skin will quickly disappear and seeds will form inside the flesh, which makes the fruit less tasty. Over-ripe fruit left hanging on the plant will inhibit further fruit production, and reduced crop yields will result.
The stem is sometimes prickly, so wear gloves and use secateurs or a really sharp knife to cut off the fruit. Unless the summer is exceptionally warm, aubergines grown under glass will be ready earlier and have a longer cropping season than those grown in the open. Cropping usually extends over four to six weeks, depending on the variety grown and the weather; in exceptionally hot summers, you may get crops for two months.