Considered a ‘herb’ when its leaves are harvested fresh, and a ‘spice’ when its seeds are the object of attention, coriander is not difficult to cultivate once you understand that it prefers to grow into cooler temperatures rather than the heat of summer. For that reason, warm and sub-tropical region gardeners should sow seed during mid-autumn to early winter while southern and cold region growers need to have seed in the ground no later than mid spring.
Prepare the garden with well rotted animal manure, rotted straw and compost, digging everything in to a fine tilth. Sow the seed in patches or shallow furrows to a depth twice the diameter of the seed. Water the ground well to promote the softening of the hard outer shell of the seed case. Coriander is notoriously slow to germinate so label your sowings well and do not despair if the first seeds take up to three weeks to come through the ground.
Prone to bolting (running to seed) when stressed, coriander needs to be grown without check. Keep the ground moist (I mulch the rows with pine needles at the same time as I sow, and water during dry spells.) If weather takes a turn for the worse and temperatures become unseasonable, cover the plants with clear plastic spread over hoops of polythene pipe, supple willow wands or number 8 wire. Failure to do this will see the leaves of the plants turn red (a sure sign it is too cold for the seedlings to take up nutrients from the ground). Stressed plants will also develop tough, tall central stalks rather than the lush, feathery foliage you are looking for. Bolting can also come as a result of seedlings being insufficiently well spaced. Thin seedlings to a spacing of 5 centimetres and feed weekly with liquid manure to encourage leafy growth.
Of course, if it is the seed you are after rather than leaf, treat your plants as harshly as you wish and harvest the seed as you see it beginning to dry on the plants. To do this, pull the entire plant from the ground, place it upside-down in a bag, and shake vigorously. Alternatively, pick in bunches and hang upside down over a carton or tray so the seeds drop in when fully ripe.
Complete seed-drying on a sunny window ledge, winnow off debris, and store seeds in sealed paper bags or envelopes. Seed can be used in cooking or re-sown in the coming season.