How to grow Florence fennel

Foeniculum vulgare · bulb fennel

Grown for its white "bulb" of swollen leaf-stalk bases with a mild aniseed flavour. It bolts easily, and then the bulb does not form or turns woody; cold spells in spring, dry soil, root disturbance, heat and long days all trigger it.

Quick facts

Type	Vegetable
Family	Apiaceae
Light	Full sun
Soil pH	6.5–8
Frost	does not tolerate frost
Soil for sowing	from 10 °C
Germination	10 days
Seedlings ready	35 days
Sowing to harvest	90 days
Where it grows	Greenhouse, Open ground, At home

When to plant

Sow for seedlings about 6 weeks before planting out.

Plant out in open ground about a week after your last spring frost, once the soil is warm.

In an unheated greenhouse everything moves about three weeks earlier.

The first harvest comes about 90 days after the shoots appear.

Frost dates · When to plant

Care

Greenhouse

Stage	Watering	Temperature	Feeding
Germination	every 2 days	10…24 °C	—
Seedlings	every 3 days	—	—
Growth	every 3 days	—	nitrogen, 28 days into the stage
Harvest	every 3 days	—	—

Open ground

Stage	Watering	Temperature	Feeding
Germination	every 2 days	10…24 °C	—
Seedlings	every 3 days	—	—
Growth	every 4 days	—	nitrogen, 28 days into the stage
Harvest	every 4 days	—	—

At home

Stage	Watering	Temperature	Feeding
Germination	every 2 days	10…24 °C	—
Seedlings	every 3 days	—	—
Growth	every 2 days	—	nitrogen, 28 days into the stage
Harvest	every 2 days	—	—

Growing notes

Light

Needs full sun in a warm, sheltered spot.

Soil

Fertile, well-drained soil rich in organic matter that stays moist, pH 6.5–8. Struggles on heavy clay.

Care

Sow 0.5–1.5 cm deep, direct or one seed per module, and plant out after the last frost 20–30 cm apart without disturbing the roots. Never let the soil dry out; give 25–50 mm of water a week. Feed nitrogen once the bulbs start to swell and earth them up to keep them white. Harvest when the bulb is 5–15 cm across, before it elongates and sends up a flower stem.

Pests and diseases of Florence fennel

White mould (Sclerotinia)

Sources

Figures checked against these sources.