Growing Fennel in the UK – From Seed & Root Division

Growing Fennel is an easy addition to your home herb garden. It will grow well, and can cope with most soils. Originating around the Mediterranean area it does prefer full sun and a bit of warmth but it’s generally easy-going.

Freshly harvested fennel bulbs with foliage attached

A hardy perennial herb, common fennel, Foeniculum Vulgare, is a member of the Umbelliferae family and it has a distinctive aniseed taste. The seeds and leaves are used for flavouring in cookery, while the stalks can be eaten raw in salad. The fat fennel bulb (which is actually swollen leaf bases) of Foeniculum Dulce can be cooked and served as a vegetable.

Growing Fennel from Seed

Fennel seeds are typically slow to sprout so it’s best to sow them early in the spring. The plants do have a tendency to bolt so, to ensure a good supply of young leaves, you may want to make successive plantings at two or three-week intervals.

Sow in temperatures of 15 to 21ºC, or outdoors after all danger of frost has passed. If sowing indoors, use compostable pots as fennel doesn’t like being transplanted. If sowing out of doors dig over the soil well and rid it of weeds. Rake the soil to a fine tilth before planting the seeds about ½” deep and 12-18″ apart. Plant at the back of a bed as fennel can typically grow to a height of 3 to 4ft. It is a good idea to keep the seed bed covered at night initially until the warmer weather.

Best Soil Types

Fennel prefers a well-drained loamy soil in full sun but will usually survive even in poor soil. If you have clay soil, add a little sharp sand to it before drilling the seeds.

Fennel needs regular watering in dry periods but don’t let it get water-logged. Fertilise it once or twice during the growing period with a general purpose product.

How to Grow a Good Fennel Bulb

Make sure you have thoroughly prepared the ground by working compost in to the soil. Sow the seeds in early summer and thin out to about 8″ apart. When the bulb is the size of a golf ball, earth it up i.e. bring soil up around the bulb to help it retain its white colour. Two to three weeks after that it will have reached the size of a tennis ball and will be ready for harvesting.

To Propagate from the Root

If your soil is light and sandy, you can propagate in autumn by dividing the roots – provided they divide easily. It’s unlikely to be possible – and you’re more likely to cause damage – if your soil is heavy or clay-rich.


Pick the young leaves and stems as you need them. The ripe seeds can be dried and stored in airtight containers for use in the kitchen. Alternatively store the seeds and sow the following year.


Fennel plants will die back over winter. If the temperature is likely to drop below -10ºC provide some protective cover.

Don’t plant near coriander or dill as this may lead to cross-fertilisation and a poor crop. Don’t plant near tomato or potato plants: they don’t like each other and hamper each other’s growth.

8 thoughts on “Growing Fennel in the UK – From Seed & Root Division

  1. Smithie says:

    I am trying to grow fennel for its bulbs (while the leaves are a bounty!) but the plants shoot upwards rather than sideways. Is there anything I can do, i.e. remove the growing tip, to ‘force’ the plant to become more bulbous?

  2. Loliss59 says:

    I’m with Smithie – I have the fennel growing in the yard and end up with more plants the next summer, and a ton of seeds that I eventually have to give away! I’d be more interested in the bulb but the roots do not grow that way. Also, the plants are over 5 ft tall!!

  3. Veg Curious says:

    I want to try growing fennel this year. I am experimenting with straw bale gardening. How close is too close to tomatoes?

  4. mamaemp says:

    My red fennel has been growing for two years. I am trying to get the bulbs to grow but I don’t know how to get them to get bigger than a golf ball. Should I dig them up at the end of the growing season to get the bulbs to grow bigger? Please let me know.

    • Herb Expert says:

      @Mamaemp. Red fennel isn’t something we’re familiar with. With bulbed fennel (ie. Florence fennel)…you can expect the bulb to swell to between 7 & 10 cm. It has to be kept warm and moist to swell. There are varieties that produce smaller bulbs however.

  5. sunskin says:

    I think I’ve been growing the wrong fennel! For 2 years I have grown it, it’s 4 ft high, I have lovely seeds and today I dug it up for the bulbs. Nothing – just roots. Have I done it wrong or is it the wrong fennel? The soil is loam, we are on chalk I think. It looks good though, just no bulb.

  6. Jobo says:

    Hi I have just gotten an allotment and there is a fennel ‘bush’ that has had nothing done to it for a year and half to two years, I am getting mixed advice as to whether to leave it alone til winter and then cut it back to others saying cut it back now to being told to dig it up and plant a fresh cutting, any advice please as am confused how, thanks

  7. Eddie says:

    Hi, I recently watched a gardening programme where a lady showed that you can prolong the life of your shop bought fennel bulb. So I put it in a glass jar in the window and the top green leaves started to grow but now the bulb is turning brown. Can I save it and plant it in my allotment??

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