Sow Florence fennel outdoors from June to July once the soil has warmed — earlier sowings are liable to bolt in the long days of spring — and harvest August to October once bulbs reach 8–10cm across. Sow in modules to avoid disturbing the taproot at transplant.
SoilCommander's step-by-step video guide to growing fennel in UK conditions — sowing, planting out, care through the season and harvesting.
A quick 60-second SoilCommander short on growing fennel in a UK garden — the essentials at a glance.
Last updated 4 July 2026
Fennel is grown either for its swollen bulb (Florence fennel) or its feathery leaves and seeds (herb fennel) — both thrive in a warm UK summer.
Not sure when to sow? See our When to Plant Fennel UK →
Sowing dates and growing advice verified against RHS guidance by the SoilCommander Growing Team.
Part of the UK Vegetable Growing Guides — how-to-grow guides for every crop.
Fennel Growing Calendar
| Task | Timing | Notes |
|---|---|---|
| Sow Florence indoors | April – May | Modules; handle roots gently at transplant |
| Sow Florence outdoors | June – July | Sow after mid-June to avoid bolting in long early-summer days |
| Sow herb fennel | March – May | Direct sow; self-seeds freely |
| Harvest Florence | August – October | When bulb is 8–10cm across |
Regional Planting Notes
The RHS notes Florence fennel "may be less successful in colder regions." Gardeners in Scotland and the north should prioritise bolt-resistant varieties (Dragon AGM, Rondo AGM), sow under cover for a head start, and hold off outdoor sowing until well into June to avoid the long-day bolting risk that catches out early sowings everywhere. This lines up with the Met Office's own finding that further north and on higher ground, the last frost can linger "well into May and, in a few places, even into June" — reinforcing why northern gardeners should favour the later end of the sowing window.
Critical: Always Use Bolt-Resistant Varieties
Florence fennel bolts before forming a bulb in most UK conditions 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 — any of these bulb more reliably than an unnamed or non-bolt-resistant strain. Do not sow before mid-April regardless of variety. Fennel also inhibits neighbouring vegetables — grow it away from other crops.
Common Fennel Mistakes
- Sowing before mid-June — early sowings bolt in the long days of spring; wait until the soil has warmed and choose a bolt-resistant variety for any earlier attempt.
- Disturbing the taproot at transplant — raise seedlings in modules rather than open trays so roots move with minimal disturbance.
- Growing in heavy, waterlogged soil — poor drainage causes bulbs to fail; grow in containers or improve drainage with organic matter on heavy ground.
- Letting the soil dry out — inconsistent moisture is a leading bolting trigger; water regularly and generously, never letting the soil dry out completely.
Frequently Asked Questions
When should I sow Florence fennel in the UK?
Sow outdoors June to July, once the soil has warmed; sowing earlier risks bolting because of the long spring day length. Harvest runs August to October once bulbs reach 8–10cm across.
Why does my fennel bolt instead of forming a bulb?
Bolting is triggered by cold spring temperatures, root disturbance at transplanting, or letting the soil dry out. Sow in modules to protect the taproot, water regularly, and choose a bolt-resistant variety such as Dragon AGM.
What are the best bolt-resistant fennel varieties?
Several UK varieties are bred or selected for bolt resistance: Dragon AGM and Rondo AGM carry the RHS Award of Garden Merit for reliable bulbing; Romanesco, Orion F1 and Victorio are also well-regarded bolt-tolerant choices widely sold by UK seed retailers; Zefa Fino is a reliable quick-maturing option alongside them.
Plan Your Fennel Sowing Window
Florence fennel bolts fast if sown too early — get the mid-June sowing reminder and harvest planner for fennel and 38 other UK crops.
Get the Garden PlannerBrowse all sowing dates: UK vegetable planting calendar · All guides: UK vegetable growing guides
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