Fennel
Foeniculum vulgare
Apiaceae · carrot family
- Matures
- 60–90 days
- Harvest
- Once · Annual
- Sun
- 6–8+ hrs
- Spacing
- 8–12 in
Planting window
When to sow, by microclimate — foggier blocks run a different calendar than sunnier ones.
| Jan | Feb | Mar | Apr | May | Jun | |
|---|---|---|---|---|---|---|
| Foggy | ● | ● | ● | ◐ | ||
| Sunny | ● | ● | ● | ◐ |
| Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|
| Foggy | ◐ | ● | ● | |||
| Sunny | ◐ | ● | ● |
Sunlight
How well it does at each level of direct sun per day.
Soil depth
Root room it needs — useful for sizing raised beds and containers.
Spacing
Room each plant needs — along the row and between rows — for sizing beds.
- In-row
- 8–12 in
- Between rows
- 8–12 in
Growth habit
The shape it makes in the bed and how tall it gets — what tells you whether to give it a trellis, a stake, or just room.
- Habit
- Upright
- Mature height
- 1–2.5 ft
Stands on its own; the tallest types appreciate a stake in wind.
How to start it
Sow it where it grows, or raise it under cover and set it out — and how far ahead to start the seedlings if it's the latter.
- Usually
- Direct-sow
- Start indoors
- 6 weeks ahead
Sown straight into the bed it will grow in.
Getting started
How it goes in the ground — how deep to sow or set it, and the soil temperature it needs to wake up. The cold-soil floor is the real limiter for direct-sowing in a foggy SF spring.
- Started from
- From seed
- Ideal soil temp
- 60°F
- Sow depth
- 0.5 in
- Time to emerge
- 7–30 days
Germinates between 50–75°F; happiest around 60°F.
Pests & diseases
What tends to trouble this crop — what it is, what you'll see, and what to do about it, least-toxic first.
Generally resistant to most diseases; aphids, thrips, and cabbage-moth larvae can chew the foliage. Manage with insecticidal soap. (Utah State Extension)
Sources
Every figure above is backed by these.
- UC Master Gardeners, Santa Clara Countybacks plantingWindow, daysToMaturity, inRowSpacing, lifecycle, harvestStyle, rowSpacing, growthHabit · UC MG Santa Clara fennel page: 'Direct seed or transplant 8 to 12 inches apart in February to April or in September to October, possibly in May or August' (spacing 8-12; the Feb-Apr & Sep-Oct = yes, May & Aug = maybe window). Days: 'harvest ... typically 60 to 90 days after transplanting'. No SF-microclimate (foggy/sunny) split source exists for fennel, so foggy and sunny carry the same Bay Area window; the South Bay runs a touch warmer than the foggy SF coast. Habit and harvest: annual, once — Florence fennel is grown as an annual for a single bulb, cut once ~60-90 days after transplanting. Between-row spacing is taken equal to the in-row figure: this crop is spaced about equally in all directions and the source gives a single spacing, not a distinct row width. Growth habit: 'Fronds of bulbing varieties typically reach 12 to 30 inches tall before harvesting, but will get taller if allowed to bloom and go to seed' (12-30 in, distinctly vertical/upright).
- Utah State University Extensionbacks sunlight, daysToMaturity, inRowSpacing, startMethod · USU 'Fennel in the Garden' (Florence fennel): 'Florence fennel prefers full sun' (full sun; 4-6 hrs = maybe). Corroborates 'thin Florence fennel to 8-12 inches apart' (spacing) and 'matures in 60 to 90 days' (days). Agronomy only; USU timing is Utah-calibrated and not used. Start method: USU Extension fennel: 'Space seeds 4-6 inches apart in the row' then thin — describes sowing in place.
- UC Master Gardeners, Santa Clara County (Containers)backs soilDepth · No fennel row; assigned moderate-depth (12-18 in) because Florence fennel forms a swollen bulb over a taproot and wants more root run than the shallow leafy greens (assigned by parity with the moderate-depth root/bulb crops).
- Utah State University Extensionbacks germination · USU Extension fennel: sow when soil 50–75°F, germinate 7–10 days; UNH green-fennel page adds 60°F / 7–30 days (optimal 60, max days 30).
- USDA GRIN Taxonomybacks botany
- Royal Horticultural Society (RHS)backs plantingDepth · RHS Florence fennel: 'make a shallow drill about 15mm (1/2in) deep'.
- UC Master Gardeners, Santa Clara Countybacks startMethod · Start method: Planting chart: Fennel carries both a Transplant row (6 weeks) and a Direct seed row.