How to Grow Fennel UK
On this page
In the UK, fennel goes in the ground early June to late July, and is ready to harvest 42–120 days after planting.
Timing is the decision that matters most in the UK: sowing early June, and that same window applies across all 4 regions covered here.
The short answer
- Plant
- Early June to late July
- Ready in
- 42–120 days
- Site
- soil pH 6.5–8
- Biggest risk
- Powdery mildew
Core growing advice on this page is checked against named horticultural sources — see References.
Fennel (Foeniculum vulgare var. azoricum)
5 sources cited · Verified
Regional Planting Calendar
| Region | Sow |
|---|---|
| Southern England derived | early June to late July |
| Midlands derived | early June to late July |
| Northern England derived | early June to late July |
| Scotland derived | early June to late July |
Rows marked derived are interpolated between regions our sources do state, because no source we consulted gives a figure for that region specifically. They are deliberately wider to reflect that uncertainty.
Southern England - detail & sources
UK-wide baseline (not yet region-differentiated): Florence fennel: sow after mid-June to avoid long-day bolting; resents root disturbance.
Midlands - detail & sources
UK-wide baseline (not yet region-differentiated): Florence fennel: sow after mid-June to avoid long-day bolting; resents root disturbance.
Northern England - detail & sources
UK-wide baseline (not yet region-differentiated): Florence fennel: sow after mid-June to avoid long-day bolting; resents root disturbance.
Scotland - detail & sources
UK-wide baseline (not yet region-differentiated): Florence fennel: sow after mid-June to avoid long-day bolting; resents root disturbance.
Quick Facts
| Factor | Value |
|---|---|
| Soil pH | 6.5 - 8 |
| Germination temp | 10°C |
| Optimal growing temp | 15-25°C |
| Minimum survivable temp | -5°C |
| Time to harvest | 42-120 days |
| Soil texture | RHS: "fertile, free-draining soil"; Florence fennel "dislikes heavy clay and waterlogged ground". |
| Drainage | RHS: free-draining, in a "warm, sheltered, sunny site". |
| Lifecycle | cool-season annual (Florence fennel) |
| Edible parts | bulb, young leaves |
At a Glance
Soil & Growing Conditions
Water: RHS: keep "consistently moist soil or compost"; containers should be checked regularly. Dry conditions are one of the triggers for bolting. Utah State: "1 to 2 inches of water per week throughout the growing season".
Soil pH range
Span reflects genuine variation between the cited authorities, not a single agreed figure.
Growth Stages
| Stage | BBCH | Notes |
|---|---|---|
| Sowing & germination | 0 | Sow about 15mm deep, rows 30cm apart. RHS. |
| Thinning & vegetative growth | 3 | Thin to 30cm apart (10-15cm for a mini-veg crop). This stage carries the highest bolting risk, from cold and shortening day length -- sow early-to-mid summer once the soil is warm, keep it consistently moist, and choose a bolt-resistant variety where possible. RHS. |
| Bulb (stem base) swelling | 4 | The overlapping leaf-stalk bases swell into the "bulb". Mound soil around them (earthing up) once they start to bulk up, to blanch the bulb whiter and sweeter. Takes three to four months in total to mature. RHS. |
| Harvest | 8 | Harvest at any size from about 5cm upward, and before the bulb starts to elongate and send up a flower stem -- once that happens the bulb toughens and the plant is running to seed. RHS. |
Harvest & Storage
When to pick: RHS: bulbs are "usually harvested when the bulb is 10-15cm (4-6in) across", though fennel "can be harvested at any size, from just 5cm (2in) upwards". Cut "before the bulb starts to elongate and send up a flower stem". Timing spans "three or four months" for full bulbs down to "about six weeks" for mini veg. RHS states no storage method. Utah State: harvest the Florence fennel bulb "when the bulbous base is less than 4 inches across and firm to the touch", with maturity at "60 to 90 days depending on variety planted".
Diseases
Pests
Florence Fennel, Sown to Bulb
Plan your Fennel planting
When to sow and plant Fennel depends on your own frost dates. Check the UK vegetable planting calendar. To work out where it fits in your beds, sketch your plot in the free Garden Layout Planner.
Growing Fennel in another region
Sowing dates, frost timing and local advice differ by country. Use the guide for where you garden.
References
5 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 fennel in the UK?
In Southern England, from early June. In Scotland, wait until early June. 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 fennel?
Sow early June to late July, at around 10°C for germination.
How long does fennel take to grow?
Typically 42–120 days, depending on cultivar and growing conditions.
What soil pH does fennel need?
A pH of about 6.5–8. 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 fennel?
Our data links 1 disease 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
How this guide is put together
The growing data on this page — sowing windows, pests, diseases, soil and site requirements — comes from named horticultural sources, listed in References below, checked against RHS and Met Office guidance. An automated pipeline assembles that verified data into the page you're reading: it selects which facts to lead with and builds the surrounding prose and layout. It does not invent a date, a source or a number — where a verified value for a field isn't available, the page leaves it out rather than guessing. A person reviews and publishes each page; nothing goes live unverified.
Related Problem Guides
Last verified 2026-08-06
Where To Go From Here
Take this crop from reading into a written plan for your own beds.
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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.