There are two main types, Florence fennel with its green leaves and bronze fennel with beautifully deep-coloured foliage.
But of Florence fennel, there are lots of varieties which have been bred for their superior taste, yield or resistance to bolting.
Try ‘Mantevano‘ or ‘Montebianco‘, both with large, white crunchy bulbs, ‘Victoria‘ or ‘Amigo F1‘, both with good bolting resistance.
The essential requirement is for a well-drained, but moisture retentive soil.
If plants suffer root disturbance, are too cold or dry out at any time they are likely to bolt and the leaf bases will fail to form.
Dig in plenty of organic matter the autumn prior to sowing and sow from April to June where the plants are to grow. Water regularly and remove weeds as they appear to prevent competition.
As plants develop apply additional organic matter such as well-rotted garden compost or manure as a layer around the plants to retain water in the soil during the summer months.
For earlier crops it is possible to sow into cell trays in a warm greenhouse in February/March and to transplant once well established, hardening off well and covering with cloches at first to keep them warm.
Similarly you can sow in the autumn and overwinter plants in the greenhouse, planting into the border in the greenhouse or polytunnel to grow on.
In either case always move the plants on while the seedlings are small and before they become pot bound.
Fennel contains good levels of potassium and some beta-carotene also vitamin Cand lots of fibre. Its antioxidants have been shown to be effective against certain cancers.
Earthing up (drawing soil up around the stems) can help to improve the whiteness of the stems.