Growing Fennel at the Allotment

Fennel has a sweet, mild, earthy flavour, making it a great addition to salads, stews, or casseroles. Growing fennel in the UK is easy, as it is a hardy plant that requires little maintenance once established. This herb dies every autumn and then re-grows in the same position once spring arrives.

Fennel comes in two popular variants, the common culinary herb and Florence fennel, grown for its edible bulb. No matter which one you want to cultivate, our tips on how to grow fennel will help you succeed.

If you want to grow fennel in your kitchen garden, this guide also covers when to plant and pick fennel, providing useful advice for both new and experienced growers.

How to Grow Fennel

Both types of fennel have a subtle aniseed flavour. Common Fennel, also called Sweet Fennel, grows tall and is mainly used as a culinary herb. Florence Fennel is grown for its bulb, which can be eaten like a vegetable.

The popular variants of the two main types of fennel are:

Common Fennel: ‘Bronze’ and ‘Wild’
Florence Fennel: ‘Dragon’, ‘Rondo’ and ‘Zefa Fino’

Growing Fennel in Summary

Sowing Fennel

Sow directly May-June
Sow in well-drained soil in a sunny spot
Thin out seedlings for Florence fennel

Growing Fennel

Water well during dry spells
Earth up Florence fennel for more white bulbs
Do not grow close to dill

Harvesting Fennel

Harvest Florence fennel August-October
Harvest when bulbs are tennis ball size
Pick leaves on common fennel as required and collect seeds once flowered

When to Plant Fennel

You can sow common fennel from March to July, and it is best sown directly outdoors, as the plant cannot tolerate root disturbances during transplanting.

Florence fennel can be started indoors in greenhouses or polytunnels from April. Transplant the seedlings outdoors in June or July, once the early potatoes have been harvested.

Before planting, harden off the seedlings and keep the module intact to protect the roots from damage during transplanting.

Tips for Growing Fennel

Both types of fennel thrive in a sunny spot with well-drained soil. Prevent the soil from drying out or becoming too cold, as the plants may bolt.
Sow Florence fennel directly outdoors in rows, approximately 3cm deep and 30cm apart. Thin the seedlings as they grow, and earth up the bulbs when they reach roughly golf ball size to produce whiter bulbs.
Do not plant common fennel near dill, as cross-pollination can affect the flavour of both plants.
Give Florence fennel enough space from other crops, and choose fertile, well-drained soil for best growth.
Water fennel regularly during dry spells to prevent it from drying out.
Tall fennel plants may need support from a stick or cane. Cut back the stems as needed to prevent the herb from overtaking your plot.
After summer, cut back faded flowers or the entire developing flower stems if you prefer to harvest only the leaves. The leaves will naturally die in autumn and regrow in spring.
Florence fennel needs to be blanched to improve its flavour.
You can gather the dry seeds in late summer and propagate them in a desired location.
Some common problems you may face when growing fennel are attacks by pests like aphids, slugs and snails, which can feed on young seedlings.

How to Harvest Fennel

Florence fennel can be harvested from August to October once the bulbs reach about tennis ball size. Cut the bulbs at the base and remove the leaves before storage or use.

Fennel seeds are typically ready for collection after the common fennel has flowered and the seed heads have fully formed. You can pick the leaves at any time, and regular harvesting encourages new growth.

The fennel sprigs can be harvested from early summer onwards, and the more you harvest, the more they grow throughout the season.

The bulbs of Florence fennel can also be frozen to extend their storage life and allow you to enjoy them beyond the growing season.

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