Because carrot seeds are tiny, they need to be sown shallowly. The trick is to keep the top-most layer of soil damp during the long germination period. Water deeply prior to planting. Direct sow the tiny seeds 5mm (¼”) deep, 4 seeds per 2cm (1″), and firm soil lightly after seeding. Make sure the seeds are only just buried. Water the area with the gentlest stream you can provide, and keep it constantly moist until the seeds sprout.