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Florence Fennel

Foeniculum vulgare var. Azoricum

Fennel being kept company by some Little Gem lettuce – late May

Human history is rich with references to the perennial herb fennel. It’s a member of the carrot family and has given its name to places all over the world. In Greek, ‘marathon’ means fennel, and the capital city of Madeira Funchal is so named because the early settlers found so much wild fennel growing – in Portuguese, the word for fennel is ‘funcho’.

Fennel is indigenous to the Mediterranean, probably where it was selectively bred to create what we know as Florence fennel. This is a smaller plant than wild fennel.

The bulb is well swollen and provides a large extra source of food from a plant that, in its wild state, grows leaves and seeds. Bulb fennel is hugely popular in India, where it accounts for half of the world’s production.

Fennel leaves catch moisture and light up the autumn garden – mid-October at Homeacres
Zefa Fino, a Florence fennel, in October – these were sown under cover in late June and transplanted in July
Micro leaves of Colossale fennel in September, on a bed of shallow compost – these have been in the greenhouse for twenty days and are now ready to eat

This lesson is about bulb fennel – a hardy annual, not the perennial herb plant. I shall just share one tip on herb fennel, such as Foeniculum vulgare ‘Purpureum’ – once established it can be difficult to remove, and the tall plants set seed prolifically, almost to become a weed.

Harvest period

  • Days from seed to first harvest: 85–120

Fennel seeds sownBulbs ready to harvestLate winter to very early springLate spring to early summerMidsummer, or just afterMid to late autumn

  • Best climate is temperate to warm, moist, or dry with irrigation.

Why grow them

Florence fennel grows fast, and in the spring it’s one of the first harvests that is not a leaf. The flavour is anise, fresh and quite strong. It works well both cooked and raw.

  • We love it roasted – it softens to a juicy tenderness and has lovely mild flavours.
  • Chopped fine in salads it brings a delicious, fresh flavour and a crunchy texture.

Fennel leaves are quite beautiful, especially in the mornings – they shimmer with gorgeous reflections. Growing a small block of fennel in any garden is good both for food and beauty.

Late October – all of these vegetables are second plantings; the fennel was transplanted ten weeks earlier
Frosty fennel after being in -1.3 °C/30 ° F conditions for five hours – the bulbs were ok, although it was borderline
Now in later November – mid-afternoon sunlight on four-month-old fennel just before harvesting, as there was an impending -3 °C/27 ° F frost

Swelling bulbs and good companions!  

Gardeners have been discouraged from growing fennel in two ways. One is a misunderstanding about its life cycle, the other is a false rumour.

  1. From spring sowings, fennel has a propensity to bolt or flower prematurely, before swelling into a nice bulb. The harvest is no bulb and many leaves.
  2. A perceived problem is fennel’s reputation for not being a good companion to other plants.

From my extensive experience, I have found this to be simply untrue.

  • Yet I see it written time and time again, which sadly puts people off growing it.

Pattern of growth

The bulbs of fennel swell fast, after a slow start. In most climates, there are two seasons of growth, divided by the flowering season in the summer.

  • You can enjoy harvests at the very beginning of summer.
  • Then the second period of harvest is through autumn and up to early winter.

Fennel’s speed of growth and small size make it a fine interplant and catch crop – see the examples below. Plants are susceptible to frost damage but are not killed by slight frost. It’s often hard to know, during the evening before a frost in late autumn, whether fennel will survive the night. Covering with fleece is a useful precaution.

Suitable for containers/shade?

Both of these are possible. However, growing in shade may draw the plant up a little, searching for light, which elongates the bulb. It’s still good to eat.

In a reasonably large container, say 30 cm/12 in wide, you could transplant four fennel. Keep them well watered, particularly as the bulbs swell.


I have grown many different varieties and do not notice a huge difference between them. Zefa Fino is sometimes a little fatter than the others, Selma a little earlier.

My go-to choice for both early and late harvests is Perfektion, which you can see in many of the photos.

Zefa Fino fennel on 7th September, from a sowing in late June
Vegetable harvests in mid-November include Perfektion fennel, celeriac, celery, leeks, kale, and carrot with root fly damage
Selma Fino fennel on 29th October – these are three months on from sowing; we transplanted them beside a trial sowing of autumn peas

sow & propagate
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Fennel is sometimes called a ‘root vegetable’. However, the bulb which interests us is actually a swelling above the main roots, in the fashion of kohlrabi and beetroot. It’s not a taproot, unlike carrot and parsnip.

This means it transplants very well, either from being sown in modules or in a seed tray, to prick out into modules.

  • Seeds germinate in seven to ten days, with long and thin cotyledons.

Sowing time

Timing is the crucial thing to get right and centres on this understanding: Florence fennel flowers in early to midsummer.

This allows time (just), from a very early sowing, for bulbs to swell before the development of a flower stem inside them. Once a stem initiates, bulbs lose their roundness and become long, thin and fibrous, rather than juicy and soft.

  1. Sow undercover, from early February on a windowsill to late February in a greenhouse with some warmth. Sowings in late winter give more time for bulbs to swell than slightly later sowings in early to mid-spring.
  2. Then do not sow again until July or midsummer. In warm climates, you can even sow in the first week of August. It depends partly on when your first frost is, because bulbs suffer damage below about -2 ° C/28 °F.

Sowing method

Raising plants under cover works really well for both early and late sowings. The reasons are:

  1. Early sowings can germinate and grow in warmth, at a time when they would not germinate outside. This allows sufficient time for bulbs to mature before midsummer.
  2. The second sowings of summer can be raised as transplants at the same time as an early vegetable harvest is reaching maturity. This overlaps their two periods of growth, which increases your growing season.

Fennel seedlings can be pricked out, and they transplant successfully. Sow in one of two ways:

  • Ether in a seed tray, from which you prick seedlings to 2.5 cm/1 in modules after seven to ten days.
  • Or sow two seeds per module and then thin to the strongest (or leave two plants, for a clump of two medium bulbs rather than one fat one).

The first leaves are tiny, therefore direct sow only where you know there to be few slugs. Take the same precautions as for sowing carrots (Lesson 8, Course 3A), with no slug habitat nearby.

Pot on?

There is no need to pot on fennel, a hardy plant that survives well as a small transplant.

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Transplant four weeks after sowing in early spring, while in late summer you can transplant just two to three weeks after the sowing date.

Transplant method

Module-grown plants often have long, thin stems, which sit well in deep planting holes. Just check that the first true feathery leaves are above surface level.


Space at an average of 20 cm/8 in, with variations according to your desired harvest.

  • Plants at 15 cm/6 in can give earlier and successive harvests of small bulbs. You must take an early harvest to thin the planting, allowing for many later harvests from the same planting.
  • Space at 25 cm/10 in for harvests of large bulbs.

Between other vegetables

The small size of fennel transplants together with the feathery nature of their leaves, which do not grab too much light from adjacent plants, make fennel an ideal interplant in both early spring and late summer. Another positive is fennel’s speed of growth, after a slow start, similar to its relative the carrot.

See the photos below, showing how this works between early spinach and late cucumber.

For the latter, we transplanted between cucumber plants whose leaves, by mid-August, were dying of mildew. There is still time from such late transplanting to have tender bulbs of 160 g/6 oz weight by October and November.

Other vegetables between

A nice example is to pop transplants of dwarf French beans, beetroot or chard between fennel bulbs, as they mature in early summer. At first the new plantings look overshadowed, but perhaps the fennel is ‘nursing’ them, through the mycorrhizal network.

  • After the fennel harvest, you twist out their main roots and the new plantings grow fast because they have already established.

I have also enjoyed success with sowing corn salad between fennel when they are about half grown. Corn salad grows slowly at first, but is well established when you harvest the fennel in mid to late autumn. It gives you salad harvests outside in winter (see Lesson 25).

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Fennel likes it moist, while also tolerating periods of dryness. During a dry spring it pays to water in May, as soon as you see bulbs starting to swell. Soil that is too dry can result in premature bolting.

Be sure to water new transplants in late summer. After that, they may not need much extra water, since they enter the water-hungry swelling phase from mid-autumn, when days are damper.

Extra mulch to retain moisture?

Only needed in arid climates, where you will also need to water a lot.

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How to judge readiness

Early growth during the first part of spring (March and April) is slow, but then accelerates as days lengthen through May. Suddenly you notice some lovely bulbs; a few may also start to elongate by early summer.

  • From the year’s first sowings, bulbing and flowering are close together in time, as fennel bulbs move so rapidly from a phase of swelling to one of flowering.
  • If you transplanted at close spacing, a first harvest could be just 90 days after the sowing date, followed by many more over the next four to five weeks.
  • In autumn, harvests are leisurely because bulbs swell slowly, with no tendency to elongate and flower.

How to pick

My preference is to rotate the bulb and remove its main roots, rather than simply cut the woody stem just above ground level. The reason for this is that new and small shoots grow from the main stem when it’s left in the soil.

If you want new shoots (which will soon flower in summer), simply cut the stem – it needs a sharp knife.

  • How much you trim the leaves and stem is entirely your choice – all of the plant is edible.
  • You can eat the roots – they have a dense texture and agreeable flavour, but it’s a small harvest.

When to pick and how often

The harvest period in early summer is only brief, so harvest a bulb or two as soon as they are large enough to eat, from about late May. Don’t expect them to grow really fat – it’s better to eat them before flowering initiates.

  • This gives a summer harvest period of two to three weeks, maybe four if the weather is cool and damp.
  • Harvests in autumn are prolonged because of day length reducing and temperatures falling. They may continue as late as December if frost holds off, with no risk of bulbs flowering.
  • If November is a mild month, they continue to fatten a fair amount, even in the short days.

Do however check for frosts in the weather forecasts. Cover plants with thick fleece before any freezing nights, unless it’s just a slight ground frost.


Another option, before frost in late autumn, is to harvest bulbs for storing. At temperatures below 10° C/50° F, fennel bulbs stay in good condition for two weeks. Beyond that they are still good to eat, except you need to trim off a couple of browning outer stalks before using them.

In summer, best keep fennel bulbs in the fridge, or as cool as you can. They stay usable for a week, while losing a little flavour and texture.

Saving seed

I have not tried this because of the space needed for several plants. From an early sowing, in a temperate to warm climate, it’s possible to have seeds by autumn.

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Which pests are likely, and when

As with its relative the carrot, fennel suffers carrot root fly, but rarely enough to harm the plants.

Slugs eat seedlings.

  • You should not need to cover with mesh against insects.
  • Lay fleece/row cover on top of seedlings, to protect early plantings from cool spring weather.
  • Then use fleece in mid to late autumn, laid on top in the evening, before any forecast of slight frost.

Other possible difficulties

Adjust sowing dates to reduce the problem of bolting – this is the main difficulty.

Frost is more about being prepared than a problem per se.


This depends on your picking method, and whether you twist out the main roots – if so, clearing is done. After removing any residual main stems, following a summer harvest, simply rake the surface level before replanting.

Or, after an autumn harvest, spread compost mulch on the bed and either plant garlic or broad beans, or leave empty until spring.

Follow with, in summer

Summer harvests give you much time ahead for new plantings. They include dwarf French beans, beetroot, late cabbage and kale, leeks and many salad plants.