Fennel

How to recognise it

Habit

Perennial, often short-lived, 1–2 m tall, with upright, branched stems from a bushy base.

Leaf

Three to four times pinnate into thread-fine segments, blue-green. Smells and tastes strongly of aniseed. The leaf base wraps around the stem like a sheath.

Flower

Flat yellow umbels 5–15 cm across made up of many small umbels, without bracts, from July to September.

Fruit/Seed

Oblong, ribbed fruits 4–6 mm long, first green, then greyish brown: the familiar fennel seed.

Stem

Round, hairless, finely striped and with a blue-green bloom.

Roots

A thick, deep taproot: that is why it transplants poorly.

Look-alikes

Dill is annual, shorter and smells of dill, not aniseed. Wild parsnip also has yellow umbels, but broad pinnate leaves and sap that causes burns on the skin in sunlight. Florence fennel is a cultivated form of the same species, with a swollen leaf base.

Flowering: July–September · Pruning: March and September

Why grow it?

• The yellow umbels, from July to September, are a magnet for hoverflies, parasitic wasps, beetles and small bees.
• Food plant for the caterpillars of the swallowtail.
• Leaves and seeds give dishes a fresh aniseed flavour.
• The airy, blue-green foliage makes a lovely see-through backdrop in a border; there is also a form with bronze leaves.
• The dry stems with their seed heads stand through winter, decorative and a shelter for insects.

Fennel: where does it grow best?

• In the wild: warm, dry, open places such as dykes, railway land, waste ground, rough ground and sunny verges, often near houses.
• Full sun.
• Dry to moist, free-draining soil; chalky or sandy is fine. It dislikes wet soil in winter.
• In the garden: a herb garden, a sunny border, a gravel garden or a butterfly corner against a warm wall.

Goes well with

• Viper’s-bugloss: Blue spikes on the same dry, sunny soil, and a bee magnet.
• Great mullein: Tall yellow candles beside the airy fennel.
• Wild marjoram: Low pink flowers at the front, for butterflies.
• Wild carrot: Another swallowtail food plant: together they attract it even better.
• Lavender: Grey leaves and purple flowers in a warm herb garden.

Fennel: when and how to plant it?

1. Buy a plant from a native plant or herb nursery, or sow. Never dig plants up from the wild.
2. Sow in April–May directly where it is to grow or in small pots; the seed needs no cold period and germinates in 1–2 weeks.
3. Transplant seedlings young and with the whole root ball: the taproot doesn’t tolerate damage.
4. Space plants 50–60 cm apart, in a sunny spot with free-draining soil.
5. Water until the plant is well established; after that it is drought-tolerant.
6. Don’t put it right next to dill: they can cross, and then your seed is no longer true.

Care

Water

Only in the first year, during drought. After that the taproot finds water deep down.

Feeding

Not needed. On rich soil it grows soft and flops over.

Self-seeding

Seeds itself freely in a warm spot. Cut off some of the umbels before the seed drops, or harvest it.

Harvesting

Pick young leaves from May to August and harvest the seed in September, when it turns greyish brown.

Caterpillars

If you see green caterpillars with black bands and orange spots on the leaves, leave them alone: they are swallowtails.

Tip: Fennel often lives only a few years. Let a few umbels ripen every year: seedlings will then take over by themselves and you will always have fennel in the garden.

Pruning and mowing

Pruning months: March and September.

When: In September, cut off the seed heads if you want fewer seedlings; in March, cut the old stems to just above the ground.

How:

• Cut the umbels when the seed turns greyish brown, and let them finish drying in a paper bag.
• Leave some stems standing over winter as shelter for insects.
• In March, remove the old stems just above the new shoots at the base.

Caution: Don’t cut back or harvest in summer if there are swallowtail caterpillars on the plant.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Sow in April–May where it is to grow or in small pots. It also seeds itself readily.

Transplanting

Division rarely works because of the taproot. Moving a young seedling with its root ball in spring is possible.

Fennel: how does it get through the winter?

Hardy to −15 °C: protect young plants.

• The leaves die back in autumn; the plant overwinters by its taproot and a bud at the base.
• Hardy to about −15 °C in dry, free-draining soil. In cold, wet soil it sometimes rots.
• The dry stems and seed heads are decorative in winter and give shelter to insects.

Diseases and pests

• Too many seedlings: In a warm, open spot it seeds itself everywhere. Cut off some of the umbels before the seed ripens and weed out seedlings young, before they form a taproot.
• Aphids: Sometimes crowded on the umbels and stems. Ladybirds, hoverflies and lacewings clear them up; otherwise hose them off.
• Rotting: A plant that doesn’t reappear after winter was usually too wet. Choose a dry, sunny spot.
• Flopping: On rich soil or in shade it grows tall and floppy. A poorer, sunny spot helps.

Through the year

• March: Cut back old stems. New shoots at the base.
• April: Sow where it is to grow or in pots.
• May: Harvest young leaves. Thin seedlings to 50–60 cm.
• June: Stems grow fast. Watch out for swallowtail caterpillars.
• July: Flowering begins.
• August: Full flower. Hoverflies and parasitic wasps on the umbels.
• September: Last flowers. Harvest seed and cut off umbels if you want fewer seedlings.
• November: Leaves die back. Leave the stems standing.

Did you know?

• Fennel is already on the list of plants that Charlemagne had grown on his estates around 800, the so-called Capitulare de villis.
• The Greek word for fennel is marathon: the plain of Marathon, famous for its battle, is said to be named after the fennel that grew there.
• Florence fennel from the greengrocer is the same species, but a cultivated form with a swollen, bulb-like leaf base.