How to Grow Florence Fennel: Planting, Spacing, Care & Harvest

Quick answer

Start indoors 4–6 weeks before the frost-free date (USU), then transplant or — preferably — direct sow at last frost. Cut bulbs when firm, about 60 to 90 days (USU). Leaf/herb fennel is covered as a section here, not a twin page. Herb fennel days-to-maturity are not sourced.

Florence fennel at a glance

PlantStart indoors: 6–4 wk before last frost; Transplant: last frost
SunFull sun; loamy well-drained soil; pH about 6.5–8 (USU).
WaterPrefer compost (USU allows up to about 1 inch per 100 sq ft); we omit printed NPK rates.
SpacingUSU: seed ¼ inch; 4–6 inches apart; rows 18 inches; thin Florence to 8–12 inches after bulbing starts.
Days to harvestMatures in 60 to 90 days, depending on variety (USU)
-7-6-5-4-3-2-1LF+1+2+3
■ Start indoors   ■ Plant out   ■ Harvest
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
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Updated

Planting dates for your ZIP: the ZIP planting planner counts each window from your local frost dates.

Organic pests and diseases: see also organic pest control. Use any product as the label directs.

Florence / bulb fennel (Foeniculum vulgare var. azoricum). Herb / leaf fennel is a section on this page only —

Florence fennel bulbs
Florence fennel bulbs. Photo: Schlaghecken Josef, Wikimedia Commons, CC BY-SA 4.0 (resized).

Planting timing (Florence)

USU: “Started fennel plants indoors 4–6 weeks before the frost-free date … then transplanted into the garden. It is best to direct seed fennel into the garden.” Seeds ¼ inch deep; soil about 50–75°F. (USU fennel) Planner: Start indoors last frost −6 to −4; Transplant last frost 0 (direct sow preferred). Succession: plant about 3–4 ft of row every 3–4 weeks (USU).

Depth and spacing

USU: seed ¼ inch; 4–6 inches apart; rows 18 inches; thin Florence to 8–12 inches after bulbing starts.

Sun, soil and water

Full sun; loamy well-drained soil; pH about 6.5–8 (USU). Keep moisture steady — stress can cause bolting or splitting. Prefer compost (USU allows up to about 1 inch per 100 sq ft); we omit printed NPK rates.

Care

Weed and keep watered. Poor drainage invites stem and root rot (NC State on fennel).

Harvest

USU: cut bulbs when firm — about 60 to 90 days. Dried umbels yield seed for herb use.

Herb / leaf fennel (same page)

UMD: “Fennel grows easily from seed planted in the garden in spring. Sow in full sun. Space rows 3 feet apart. Thin plants 10 to 12 inches apart.” Harvest ripe seeds; tender flower stalks are edible. (UMD fennel) NC State: sow directly in spring; plants freely self-seed — remove spent flowers to limit spread. (NC State Foeniculum vulgare) No herb-fennel days-to-maturity integer is sourced here — we do not invent one.

Pests and diseases

USU: aphids, thrips, cabbage moth larvae; bolting under water or root stress. NC State: aphids, slugs; stem/root rot in wet soils. Prefer drainage and cultural controls; aphids: soap or oil as labeled (UC IPM).

Related: ZIP planner · organic pest control · all grow guides

Frequently asked questions

When do I plant Florence fennel?

Start indoors 4–6 weeks before the frost-free date; transplant or prefer direct sow at last frost (USU).

Is leaf fennel a different page?

No — it is a section on this URL only.

How long to bulb harvest?

About 60 to 90 days (USU).

More grow guides: All grow guides

Sources