Fennel
Sweet Fennel, Common Fennel, Bronze Fennel, Fennel
Perennial in mild climates; grown as annual in cold zones. Allelopathic — inhibits growth of many vegetables, especially tomatoes and beans. Best planted in isolation or at garden edges. Highly attractive to swallowtail butterfly larvae and beneficial insects. Direct sow; taproots resent transplanting. Self-seeds freely. Both foliage (herb fennel) and swollen bulb (Florence fennel) are edible.
- Germination
- 7–14 days
- Soil temperature
- 13–24 °C
- Harvest after sowing
- 65–90 days
- Spacing
- 30–45 cm
When to plant fennel
Sow outdoors from 2 weeks before to 2 weeks after your last spring frost.
Dashed line: typical last spring frost in zone 7 (Apr 5). Zone dates are averages; most of the UK is zone 8–9, central Europe 6–7 and the Baltics and Scandinavia 4–6. In the app, Tomatograph uses your garden's own frost dates.
How to grow fennel
- 1
Sow in place
Herb fennel has a taproot and dislikes being moved. Sow direct around the last frost, or in early autumn in mild areas.
- 2
Keep it apart
Fennel holds back the growth of many neighbours, especially tomatoes and beans. Plant it at the edge of the garden, and away from dill to avoid cross-pollination.
- 3
Grow on
It needs little care once established and attracts beneficial insects. Swallowtail caterpillars may feed on it.
- 4
Harvest
Snip the feathery leaves from about 65 days and collect the seeds once they turn brown. It self-seeds freely if left.
Growing conditions
Light
Full sun
Water
Low water
Temperature
-5–32 °C
Frost tolerance
Frost-hardy — tolerates frost
Days to maturity
65–90 days
Ideal soil pH
7.5–8
How Tomatograph watches your fennel
Tomatograph checks your local forecast every morning and only speaks up when one of these applies to your garden.
- First frost within 14 daysReminder to mulch the roots before winter.
- 3 days at 35 °C or aboveHeat-wave alert while plants are flowering or fruiting: shade and water early.
- Humidity above 80% for 48 hoursCheck for root rot, which thrives in those conditions.
- Within a week of maturityHarvest-window reminder based on when you planted.
Fennel questions
- When should I plant fennel?
- Sow outdoors from 2 weeks before to 2 weeks after your last spring frost.
- How long do fennel seeds take to germinate?
- Usually 7–14 days at a soil temperature of 13–24 °C.
- How long until I can harvest fennel?
- About 65–90 days after sowing, depending on variety and weather.
- How far apart should I plant fennel?
- Allow 30–45 cm between plants.
- What grows well with fennel?
- Good neighbours include dill.
Growing guide written by Tomatograph. Planting figures from openplantdb (CC0 1.0). Zone frost dates are averages from openplantdb (CC0 1.0).