How to grow Florence Fennel

Where to plant

Grow Florence fennel in full sun in loose, loamy soil with plenty of compost worked in. It needs more fertile soil and steadier moisture than the herb fennel does, because any check to growth from dry soil or heat pushes it to flower instead of forming a bulb.

Timing matters more than anything else. Florence fennel bulbs best in cool weather, and in hot weather it turns woody and tends to bolt.

• Florida, the Gulf South, Texas and the Desert Southwest: sow from fall into winter so the bulbs swell in the cool months, and finish before spring heat.
• Southern and Northern California: sow from late summer through winter for a cool-season crop.
• The Mid-Atlantic, Southern Plains and Mid-South: sow in early spring and again from August. Sowings in July heat tend to bolt before they bulb.
• The Northeast, Midwest, Mountain West, Northern Plains and Pacific Northwest: sow in spring once the soil is workable, and again in midsummer for a fall crop, since plants take light frost.
• Alaska: sow in late spring and early summer for a summer crop.

Choosing a variety

Choose a true bulbing variety sold as Florence fennel or finocchio. Utah State University Extension names 'Zefa Fino' and 'Orion' as compact varieties that form thick bases and resist bolting, which makes them a good choice for spring sowings.

How to plant

1. Direct sow where possible, as fennel has a taproot and does not like being moved. You can also start seed indoors 4 to 6 weeks ahead and transplant carefully while small.
2. Sow seed about 1/4 inch (6 mm) deep when the soil is between 50 and 75°F. Seedlings usually appear in 7 to 10 days.
3. Space seeds 4 to 6 inches apart in rows about 18 inches apart, then thin to 8 to 12 inches (20 to 30 cm) apart as the bases begin to swell.
4. For a steady supply, sow a short row every 3 to 4 weeks through your sowing window.
5. As the bulbs swell, you can mound soil up around them to keep them pale and mild.

Watering and feeding

Water regularly and do not let the soil dry out between waterings. Drip irrigation and mulch both help keep the moisture even. Dry spells are the most common reason plants bolt or the bulbs split.

Work compost into the bed before planting and use a soil test to guide fertilizer. Fennel needs a moderate amount of nitrogen and little phosphorus or potassium, so a light side-dressing of nitrogen once the bulbs start to form is usually enough.

Pruning and care through the year

• Keep the bed weeded, as young fennel competes poorly.
• Fennel flowers attract bees and many beneficial insects, but in mild climates fennel reseeds freely. Pull bolted plants or cut the flower heads before they set seed.
• Wild fennel is rated a moderate invasive plant in California by the California Invasive Plant Council, so in California and other mild areas never let your plants go to seed near open land.

Harvesting

Harvest when the bulb is firm and about the size of a tennis ball, usually 60 to 90 days from sowing, and before the plant starts to send up a flower stalk. Cut it off at the base. Small shoots often regrow from the root and can be eaten while young.

The fronds can be snipped and used fresh at any stage. They do not keep their flavor well when dried.

Growing in pots

Florence fennel can be grown in a large, deep container, but its taproot makes it happier in the ground, and pots dry out quickly, which leads to bolting. Water containers often.