Sweet Fennel (Foeniculum vulgare var. dulce)
1 sources cited · Verified
The short answer
- Plant
- Mid April to late May
- Site
- 6+ hours of sun, soil pH 6–7.5
- Biggest risk
- Root rot
In the UK, sweet fennels go in the ground mid April to late May.
Sweet fennels (Foeniculum vulgare var. dulce) — perennial.
Timing is the decision that matters most in the UK: there are 4 separate regional sowing windows, ranging from mid April in Southern England to mid April in Scotland.
Core growing advice on this page is checked against named horticultural and university-extension sources — see References.
Regional Planting Calendar
Quick Facts
At a Glance
Soil & Growing Conditions
Growth Stages
Harvest & Storage
Diseases
Pests
Sweet Fennel, RHS's Third Foeniculum Variety
References
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A vigorous herbaceous perennial with finely divided, feathery, bright green foliage and somewhat swollen leaf bases (though not as bulbous as traditional Florence fennel). Grown primarily as a culinary herb for its aromatic leaves and aniseed-flavoured seeds. Not native to GB/Ireland. Hardiness H5 (hardy in most UK locations, even during severe winters). Full sun, tolerates south-, east- or west-facing aspects. Soil: chalk, clay, loam or sand; moist but well-drained or well-drained; acid, alkaline or neutral pH. Height 1-1.5m, spread 0.5-1m. Time to maturity 1-2 years. Propagate by seed. Pests: aphids, slugs. Diseases: root rots, powdery mildews. Foliage and seeds are edible; remove faded flowers to prevent unwanted self-seeding. RHS explicitly distinguishes this variety from both the already-published Herb Fennel (var. vulgare, no swollen leaf base) and Florence Fennel (var. azoricum, a much more pronounced bulb) -- sweet fennel sits between the two, with somewhat swollen leaf bases that are not as bulbous as Florence fennel's.
1 independent sources are cited for this crop. Where they disagree - soil pH is the clearest case - every figure is preserved rather than averaged into false precision.
Frequently Asked Questions
When should I sow sweet fennels in the UK?
In Southern England, from mid April. In Scotland, wait until mid April. Treat these as a guide rather than a fixed date — the governing rule is to sow only once frost risk has passed and temperatures are reliably warm enough.
When do I sow sweet fennels?
Sow mid April to late May.
What soil pH do sweet fennels need?
A pH of about 6–7.5. That span reflects genuine variation between the authorities we cite rather than a single agreed figure — the References section lists each source's exact range.
What problems affect sweet fennels?
Our data links 2 diseases and 2 pests to this crop. See the sections above for each one and how to manage it.
Plan next season before the problems start
Most of the advice on this page comes down to timing and spacing — sowing at the right moment, rotating beds, and giving plants enough airflow. The UK Garden Planner lays your plot out month by month so those decisions are already made before the season starts.
Get the UK Garden Planner →Instant PDF download · Written for UK growing conditions
Last verified 2026-08-29
Where To Go From Here
Take this crop from reading into a written plan for your own beds.
Plan the next step
Use the printable SoilCommander planner for your region to turn this guide into sowing dates, bed layouts and weekly garden tasks.