Fennel the vegetable or Fennel the herb?
There are two sorts of fennel: one is classed as a herb and the other a vegetable.
The vegetable - Foeniculum dulce - swells at the base to produce a vegetable with a strong aniseed flavour. This is the one you can slice into your salad or smother in cheese sauce and bake into a delicious gratin. This is the one we are talking about today.
Florence Fennel is a tricky customer. It thrives on warm, moist, fertile, sandy soils. However, it is prone to bolting and sensitive to day length. You need to be on the ball with watering and make sure fennel is first in the queue so that it never dries out. Otherwise, it will decide it needs to flower and bolt with lightening speed the moment your back is turned. Always look for bolt resistant varieties to give yourself the best chance of success.
Because of its sensitive to day length the best time to sow is in mid June for an autumn crop. You can try sowing earlier (April-May) but because of the shorter days and higher risk of a sudden temperature drop it is more likely to bolt.
So, choose an open, sunny site and pray for a long, hot summer. If you are organised prepare the bed by adding plenty of well-rotted organic matter the winter before you plant.
The plants dislike root disturbance and don't transplant well from standrd pots. However, sowing single seeds into Rootrainers will allow you to transplant without this root damage. When your seedlings are established simply open the Rootrainer a little to take a peek at their roots. Plant out when you see a good set of striaght roots.
Or you can plant seeds direct into the ground. To do this water the soil really well first. Then plant 15mm (½in) deep in rows 30cm (12in) apart. You can either, set three seeds together at intervals in a row and thin the seedlings to leave the strongest one. Or, you can sow seed thinly along a drill and thin after. Whichever you choose, thin to 30cm (12in) apart in the rows when the soil is warm from May to July.
Water well throughout the growing season, keep weed free and mulch to conserve moisture. Feed with high potassium fertiliser every two weeks once established.
As the bulbs begin to swell from mid summer, you will need to earth them up (as you would with potatoes). This will protect from early frost and leave you with blanched, tender white bulbs.
Fennel will tollerate light frost, but will not survive outside through any but the mildest winter.
If you plant in late June then you sould be able to harvest your bulbs in mid to late October. They will be ready for harvesting when the bulb is about 7-10cm (3-4in across). Cut them 2.5cm (1") above the ground. If you are lucky, they may sprout feathery shoots from the cut bulb. You can use these as you would use herb fennel to flavour fish dishes etc.
Pest & Diseases
Bolting: Try and head it off at the pass by using only bolt-resistant varieties. Sow or plant at the correct time and keep the soil or compost moist at all times. Don't let them go thirsty!
Slugs and snails: These mini predators love fennel seedlings. Use the usual Slug Buster beer traps or stage a midnight intervention and pick off any heading toward your plants.