How to grow fennel (bulb)

Foeniculum vulgare var. azoricum · Apiaceae · Vegetable

Fennel (Bulb) is a cool-season vegetable in the Apiaceae family, grown either from a direct sowing or from transplants. It wants full sun (six or more hours of direct light) and steady, even moisture. From sowing to first pick is about 65–90 days. It shrugs off a light frost but a hard freeze will damage it.

Grower’s note: Bulb (Florence) fennel bolts in heat and after a cold snap, so the fall crop is far more dependable. Hill soil around the swelling base to blanch it. It hinders many neighbours - keep it in its own corner, away from dill and coriander (they also cross-pollinate).

Sowing

Sow about 0.25″ deep, into soil between 60–80°F — germination is quickest near 70°F. Germination takes a week or two (7–14 days). For an early crop, start seed indoors about 4 weeks before your last spring frost and grow it under bright light.

Spacing & layout

Give each plant about 8″ along the row with roughly 18″ between rows. On a square-foot grid that is 4 per square foot. Allow at least 12″ of loose, workable soil for the roots. It grows well in containers at least 12″ deep.

Fitting it to your season

As a cool-season crop, fennel (bulb) does its best growing in the mild weather of spring and fall and tends to bolt or turn bitter in summer heat. A second sowing in late summer, timed to mature as the weather cools, is usually the better crop of the year — though a hard freeze will end it.

Quick facts

When to plant fennel (bulb)

Companions

Common problems

Pests: black swallowtail caterpillar, aphids.

Diseases & disorders: cercospora leaf spot, root rot.

Same family (Apiaceae)

Rotate these so they don’t follow each other in the same bed year to year.

Figures are typical home-garden ranges from Cooperative Extension planting guides, cross-checked against multiple state sources. Your variety and conditions will vary.