Foeniculum vulgare subsp. vulgare var. azoricum

Bulb Fennel

Fennel is both a herb and vegetable it is from the same family (Apiaceae) as carrots, celery, and parsnips (along with some other herbs). It is often grown as a winter vegetable and commonly, although incorrectly, known as a root vegetable.

If choosing to grow bulb fennel make sure you select Foeniculum vulgare subsp. vulgare var. azoricum because this is the one that has the large bulb-shaped base.

There are also other fennels which are grown as herbs and these include green fennel Foeniculum vulgare subsp. vulgare var. dulce and red fennel Foeniculum vulgare subsp. vulgare 'Rubrum' (a more decorative cultivar). Herb fennels can reach 6 to 8 feet in height whereas bulb fennel only grows to about 2 feet (60cm).   

Uses

You can start harvesting fennel as soon as it is about 7.5cm wide, any larger and fennel tends to become stringy. Just cut the bulb off at the base of the plant along with some of the base plate (just above the root system – you may need to expose the roots by removing soil from around the base of the plant. Wash the bulbs, dry and store in a airtight plastic bag for up to a week under refrigeration. 

Culture

Once established, plants don't require too much watering but the soil should be kept moist. Lay mulch to conserve soil water. Leaves can be harvested at any time but some growers suggest that harvesting leaves of the bulbous type discourages the bulbous base from thickening to it optimal size. As the plant grows mound up the soil onto the bulbous base. This has the effect of blanching the stalk. The best time to harvest the bulbs is in autumn or spring when they're about 7 to 10 cm thick. Avoid planting near dill as they readily hybridise.

Fennel bulbs can be sliced thinly and added to salads. They can also be boiled, steamed or grilled and served with butter or cheese. 
Some newer types include Florence fennel cultivars which are resistant to bolting. 'Perfection' has a medium sized bulb and mild aniseed taste, 'Cantino' has a slightly stronger aniseed flavour and 'Amigo' has flatter shaped bulbs. 

Well prepared soil with no further additions required. 

Propagation

Seeds may be sown directly into the veggie patch when there is no longer a risk of frost. In cooler regions you can start them off in late autumn in a cold frame or greenhouse and plant out once temperatures have started to warm up (but early spring). Don't let them get much taller than about 15cm before transplanting otherwise the taproot will be very long and they may take a while to become established. 
Rows should be about 0.9 to 1.0m apart and plants about 30cm apart in the rows.