In the UK, sow Florence fennel outdoors in June or July — sowing earlier risks bolting in the long, cool days of spring. Bulbs are ready to harvest August to October, once 8–10cm across.
Last updated 4 July 2026
Florence fennel bolts easily in the UK — timing is critical. Here's when to sow, which varieties to choose, and how to avoid the most common failure.
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Sowing dates and growing advice verified against RHS guidance by the SoilCommander Growing Team.
Part of the UK Vegetable Planting Calendar — see all sowing dates and monthly guides.
Florence Fennel Planting Calendar
| Task | Timing | Notes |
|---|---|---|
| Sow Florence indoors (bolt-resistant) | April – May | Individual pots; handle roots gently at transplant |
| Sow Florence outdoors | June – July | Sowing before mid-June risks bolting in long spring days; south England favoured for warmer summers |
| Harvest Florence | August – October | When bulb is 8–10cm across; earth up to blanch |
Regional Planting Notes
The RHS notes Florence fennel “may be less successful in colder regions and heavy clay soil” — cold spring snaps being a key bolting trigger, and the Met Office notes these can persist into May, or even June, further north. Gardeners in Scotland, northern England, or on heavy ground get the most reliable bulbs by sticking to bolt-resistant varieties and sowing at the later end of the June–July window.
Critical: Always Use Bolt-Resistant Varieties
Standard fennel bolts before forming a bulb in the UK unless you choose a bolt-resistant variety. Well-known bolt-resistant Florence fennel varieties include Romanesco, Orion F1, Victorio, Dragon AGM, Rondo AGM, and Zefa Fino. Do not sow before mid-April regardless of variety.
Common Mistakes to Avoid
- Disturbing the taproot at transplant. Florence fennel resents root disturbance — sow into individual modules or pots rather than pricking out seedlings.
- Letting the soil dry out. Water regularly and generously; the RHS warns never letting the soil dry out completely, since drought stress is a major bolting trigger.
- Sowing outdoors before mid-to-late June. Early outdoor sowings hit the long, cool days of spring, which trigger bolting instead of bulb formation.
Frequently Asked Questions
Why does my fennel bolt instead of forming a bulb?
Cold spring temperatures, root disturbance at transplanting, dry soil, and sowing too early are the main triggers — delay outdoor sowing until June and keep watering consistent.
Which Florence fennel varieties resist bolting best?
'Dragon' AGM and 'Rondo' AGM carry the RHS Award of Garden Merit for bolting resistance. Romanesco, Orion F1 and Victorio are also well-regarded bolt-tolerant varieties widely sold by UK seed retailers, and Zefa Fino is a reliable quick-maturing option alongside them.
Is Zefa Fino a good choice for UK gardens?
Yes — it's a quick-maturing variety producing medium to large bulbs, a reliable option alongside the AGM varieties Dragon and Rondo.
Plan Your Fennel Sowing Window
Sow too early and fennel bolts before it bulbs — get the mid-June reminder and harvest planner for fennel and 38 other UK crops.
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