Roots
They want light, stone-free soil that has not been freshly manured.
Sow very thinly, 1cm deep, so that you hardly need to thin: the smell of thinning brings carrot fly. Early varieties can go in under fleece in March; sow maincrop from April to early July. Keep the seed bed damp until they are up, which can take three weeks.
Pull the biggest first. Maincrop carrots can stay in the ground under straw until Christmas on light soil.
What goes wrong
Maggots tunnel in the roots. Cover the crop with fine mesh from sowing, or surround it with a barrier 60cm high.
Stones, or fresh manure. Grow them in last year's manured bed.
The seed bed dried out. Water the drill before sowing.
Good neighbours: Onions, Leeks, Chives.