Timing
Direct sow April to mid-July for harvests from July to November. Direct sow winter-harvest carrots in the first two weeks of August. Sow at 3 week intervals for a continuous harvest. Optimal soil temperature: 7-30°C (45-85°F). Seeds take as long as 14-21 days to germinate.

Starting

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.

Growing

Ideal pH: 6.0-6.8. The softer and more humus-based the soil, the better. When soil is dry enough in spring, work it to a fine texture. Broadcast and dig in ½ cup complete organic fertilizer for every 3m (10′) of row. Avoid fresh manure. Carrots will become misshapen, but still edible if they hit anything hard as they grow down into the soil. Keep weeded and watered.
It is very important to thin carrots in order to allow them room to grow, and so they don’t compete for available nutrients, moisture, and light. Then to 4-10cm (1½-4″) when the young plants are 2cm (1″) tall. Use wider spacing to get larger roots. As they grow, carrots push up, out of the soil, so hill soil up to prevent getting a green shoulder.

Here are some more good tips on how to grow carrots from seed.

Harvest

Carrots can be harvested at any size, but flavour is best when the carrot has turned bright orange. After harvest, store at cold temperatures just above 0ºC. You can store in sand or sawdust, or simply leave carrots under heaped soil in the garden during the winter, and pull as you need them.