Plants grow up to 1 metre, with dill-like plumey leaves, aromatic yellow flowers and a bulbous stem. Fennel has an aniseed flavour and all parts of the plant can be used.
While sweet fennel is prized for its bulb, other varieties – some quite weedy – have been developed for their stalks or decorative foliage and it is easy to confuse young plants prior to bulb formation.
Fennel prefers rich well-drained soil and full sun. It is not keen on heavy or compacted soils.
To plant, sow seeds directly once the ground is consistently warm. Planting in mid-summer should give a harvest in autumn.
Seeds should be spaced (or seedlings thinned to) at least 25cm apart and covered lightly with about 1cm of soil. Seeds can be sown in trenches to assist blanching later on. Germination takes 7-10 days – keep soil moist during this period.
Once the stem has swelled to the size of a golf ball, it can be blanched to reduce bitterness and encourage a clean white bulb at harvest.
Put a paper or cardboard collar around the base and mound soil around the collar. Once the stems have swelled to double the size (around 1 month after blanching), they are ready for harvest.
To harvest bulbs, remove collars and soil from the base and cut just above the root with a sharp knife.
Harvest the leaves at any time, remembering to leave enough to feed the plant.
Harvest seeds once they have formed and the flower head has died. Store seeds in a cool dry place. Note that different varieties cross-pollinate readily with each other, with the weedy fennel and also with dill.
Snails and slugs are fond of the bulbs, so check before eating. Although fennel is very hardy, excessive heat, cold, disturbance or water stress can affect cause plants to bolt. If left too long, fennel becomes stringy and tough.