Fennel is a crop that can be grown in modules and then planted out when earlier crops have been cleared. It can be sown for an early crop but spring/early summer is it's period for producing seed so best to wait until after mid-summer's day before sowing.
Sow in modules, in late June, as we did for earlier crops, about 10-15mm deep. Plant out 15-20cm apart in rows 30cm apart three to four weeks after sowing. You will need 6-8 plants for a single row.