Florence Fennel

Florence fennel is a variety of Foeniculum vulgare grown for its enlarged, flattened stem bases, which form a bulb eaten as a vegetable. The bulbs can be eaten fresh in salads or cooked by roasting, grilling, or sautéing. Accounts differ on its life span: one describes it as a cool-season annual, while another calls it a biennial to short-lived perennial.

Sowing. Sow seed directly in the garden about ¼ inch (6 mm) deep. Sow after the last spring frost, or in mid-summer for a fall crop. Sowing from midspring through early summer is also listed, but planting right after the first frost can bring bolting in summer heat. For a fall harvest, seeding from mid-June to July lets the bulbs develop in cooler, shorter days.

Starting indoors. Seed can be started indoors 4 to 6 weeks before the last spring frost. Direct sowing often works better, since Florence fennel is sensitive to transplant shock.

Germination and thinning. Seeds usually germinate in about 7 to 10 days. Once plants begin to bulb, thin them to 8 to 12 inches (20 to 30 cm) apart.

Site and soil. Florence fennel grows best in full sun and loamy soil rich in organic matter, with a pH of 6.5 to 8.

Watering. Keep the soil evenly moist, since dry conditions push plants to bloom instead of forming bulbs. Do not let the soil dry out between waterings.

Weeds and mulch. Control weeds while plants are young, and mulch with straw or lawn clippings to limit weeds and keep the soil cool and moist.

Blanching. Mound soil around the swelling bulbs to keep the bases paler and more tender. Some accounts suggest starting when the bulbs are about the size of an egg.

Fertilizer. Avoid high-nitrogen fertilizers, and use a soil test to guide any feeding.

Bolting. Hot summer temperatures, long days, and plant stress can make Florence fennel bolt, or flower early, which lowers bulb quality. Plants that are short of water or nutrients also form small bulbs. Newer slow-bolting varieties are a good choice.

Pests. Aphids, thrips, and cabbage moth larvae can damage leaves, which leads to smaller bulbs. Aphids can be washed off with a strong stream of water.

Root rot. Fennel has few pest problems other than root rot in very wet soils.

Harvest. Pick bulbs when they are about the size of a tennis ball. Another account says to harvest when the base is less than 4 inches (10 cm) across and firm to the touch. Lift the plant, trim the roots, and remove excess top growth.

Storage. Keep bulbs in a loosely tied plastic bag in the refrigerator for up to 5 days. Bulbs do not freeze well and do not store well for long periods.

Pets. Fennel is listed as non-toxic to cats and dogs. Small amounts in food are low risk, but concentrated oil should be avoided.

Skin. The plant sap can irritate the skin of sensitive people, especially in sunlight.