How to Grow Fennel From Seed

Florence fennel grows best in cool, steady weather, so timing matters. Direct-sow it in early summer once the soil has warmed past about 60F, or in mid to late summer for a fall crop, which is often the sweeter, more reliable harvest. Very early spring sowings tend to bolt before they bulb, so hold off until the weather settles. Because it dislikes root disturbance, always sow it right where it will grow rather than starting it in trays.

Fennel has a taproot and hates being transplanted, so direct-sow it in full sun in rich, well-drained soil. Sow the seeds about a quarter inch deep, in clusters of two or three every 4 to 6 inches, and keep the soil evenly moist at around 60 to 70F. Seedlings appear in about 7 to 14 days. Thin them to one strong plant every 6 to 12 inches so each has room to swell a full bulb.

The secret to a good fennel bulb is never letting it check its growth. Water regularly so the soil stays evenly moist, since dry spells and heat both trigger bolting. As the base begins to swell, mound a little soil around it to keep the bulb pale, sweet, and tender. A light feed keeps growth strong. Give fennel its own corner of the garden, as it can hold back many of its neighbors, and keep it away from dill and coriander in particular. Climate decides your timing. In the North and Midwest, sow for a fall harvest so the bulb swells as the weather cools, since summer heat makes it bolt fast; in mild-winter states like California, Arizona, and the Gulf Coast, grow it through fall and winter, when the cooler months give the sweetest, densest bulbs.

Fennel is famously independent and grows best with a little space of its own, but a few plants make good neighbors by drawing pests away and pulling in beneficial insects. These four pair well, and you can add any of them in one click:

Harvest the bulbs once they are plump and firm, usually around 80 to 100 days from sowing, by cutting them off at the base. Leave the roots in and you may get a few tender secondary shoots. Snip the feathery fronds any time as a herb, and if you let a plant flower and set seed, gather the ripe seed heads when they turn brown to use as a spice.

Florence fennel is a three-in-one plant. The crisp, anise-sweet bulb is delicious shaved raw into salads or roasted until caramelized. The feathery fronds work like a herb, scattered over fish, potatoes, and dressings, and the ripe seeds become a warm, licorice-scented spice for sausages, breads, and pickles. Few vegetables give you the bulb, the herb, and the spice from a single sowing.

• Bolting before bulbing: caused by heat, dry soil, or root disturbance. Sow in early or late summer, water steadily, and pick slow-bolting varieties.
• No bulb forming: often too little water or too much competition. Keep the soil moist and thin plants so each has room.
• Poor germination: keep the soil evenly moist and warm, around 60 to 70F, and do not sow the seeds too deep.
• Stunted neighbors: fennel can inhibit nearby vegetables, so give it its own spot rather than crowding it into a mixed bed.