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How to grow fennel

Mature fennel plants growing in an allotment.  Mature fennel bulbs ready for harvesting

An alotment in Bournemouth with a good crop of fennel (left); fennel bulbs ready for harvest (right).

Some vegetables deserve to be more popular than they are, and Florence fennel is certainly one of them. A defining ingredient in Italian cooking, it is a gourmet’s treat that is prized mainly for the engorged bulbs that form just above the soil surface.

Like the proverbial elephant described by blind men, the bulbs produced by fennel are the sum of quite unrelated parts. Anatomically, they are formed from the thickened, overlapping bases of leaves and have the same layered construction of an onion. The texture is crunchy and stringy like celery, and the flavour is similar to that of anise or licorice. Somehow, defying all logic, the differences are magically reconciled to create a desirable vegetable of sublime elegance.

A growing concern

Fennel is closely related to carrots, and like them, its seeds are very slow to germinate.

Fennel seed  is slow to germinate

Fennel seed is slow to germinate.


Given this idiosyncrasy, a crop is easier to establish from transplanted seedlings rather than from seed sown directly into the ground. To produce transplants, just sow seed in compost-filled module trays from March to July.

Fennel seedling ready for transplanting Fennel seedlings raised in modules and ready for transplanting

Fennel is best started by sowing into modules and transplanting the seedling when the roots have filled the cell.


Pest and weed problems associated with crop establishment are then avoided, and the only thing that remains is keeping the compost moist at all times. Transplanting can commence five weeks or so after sowing, when the roots have filled the cells and the seedlings are about 10cm tall.

Transplanting fennel seedling 6cm

Fennel seedlings can normally be transplanted about five weeks after sowing.


When they are transferred to the ground, leave about 20 cm between seedlings each way and dose them with water to settle the soil around the roots.

Fennel seedlings just transplanted out Fennel should be planted about 25-30 cm apart.

Fennel should be planted about 20 cm apart.


Other than the usual troika of pests – slugs, snails and rabbits – fennel is remarkably trouble free. Once the pests are under control, all you then need to do is follow two essential rules: keep the soil moist and maintain weed control. Bolting can be a problem, especialy with early sowings made when temperatures are low. Avoid disturbing the roots when transplanting seedlings, and keep the plants well-watered throughout their lives. Some varieties are prone to bolting, so choose those with more resistance.

Italian gardeners living in England ridge soil around the bulbs to blanch them, and if you want to do the same, wait until they put on some size and swell up before commencing. Blanching, however, isn’t really necessary, and personally, I think it involves way too much work.

Fennel bulb being blanched

Some gardeners put soil around the bulb to blanch their fennel, but this is not necessary as the bulbs will naturally produce white flesh.


Harvesting can begin once the bulbs are about 8 to 10 cm in diameter. A quick and brutal method is to pull the bulbs up for a once-off harvest of each plant.

Fennel var. Rondo bulbs harvested with roots  

Fennel var. Rondo bulbs harvested by being pulled up.


My favourite way, however, gives two crops from the same plant and involves slicing through the bottom of the bulb with a sharp knife, leaving a small, flat stump about 6mm thick.

harvested fennel cut high leaving a stubble for regrowth

Fennel bulbs harvested by slicing through the bottom of the bulb with a sharp knife.


If done correctly, new plants will sprout from the stump, yielding a crop of baby bulbs.

Regrowth producing new bulbs from an old fennel root  Baby bulbs of fennel regrown from old fennel roots

Regrowth from an old fennel root.


Cooking up a storm

After the plants are harvested, trim off the tops and eat the bulbs raw in a mixed salad or on their own thinly sliced and simply dressed with lemon and olive oil. Alternatively, cut the bulbs in half lengthwise and braise them in water with either olive oil or butter. Heaven.

Under no circumstances should you let the rest of the plant go to waste. The tall, thin stems just above the bulbs can be cut up and thrown into soups and gravies to add extra flavour – they are quite tough, so remember to remove them before serving. The fine leaves topping the stems are a particular treat either chopped up and sprinkled over cooked vegetables and pork chops or added to a tomato-based pasta sauce just before serving. The anise flavour is real plus that lifts dishes to a new level.

Because Florence fennel is not especially popular, don’t expect to find a huge number of varieties in seed catalogues. Despite the limited choice, however, there are some decent ones worth tracking down, such as Rondo, a modern hybrid that is very bolt resistent, reliably producing fat, rounded bulbs of exceptional quality. Another fairly good one is the non-hybrid Zefa Fino, with bulbs that are somewhat flattened and seeds that are relatively inexpensive.

Rondo is a variety of fennel that produces fat bulbs of exceptional quality

The variety Rondo produces very high quality, fat, rounded bulbs.


Once watering and weeding are sorted, Florence fennel is easy to grow and great to eat. Two harvests are possible from the same sowing, and nothing goes to waste. With so much going for it, it’s a puzzle why fennel isn’t more popular.




© Michael Michaud

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