Fennel (Foeniculum vulgare var. azoricum)
5 sources cited · Verified
The short answer
- Ready in
- 42–120 days
- Site
- soil pH 6.5–8
- Biggest risk
- Powdery mildew
In the UK, fennel are ready to harvest 42–120 days after planting.
Fennel (Foeniculum vulgare var. azoricum) — cool-season annual (Florence fennel).
Core growing advice on this page is checked against named horticultural and university-extension sources — see References.
At a Glance
Quick Facts
| Factor | Value |
|---|---|
| Soil pH | 6.5 - 8 |
| Germination temp | 10C |
| Optimal growing temp | 15-25C |
| Minimum survivable temp | -5C |
| 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 |
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
References
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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
How long do fennel take to grow?
Typically 42–120 days, depending on cultivar and growing conditions.
What soil pH do 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
This page gives you the thresholds; the planner turns them into your own calendar. It works from what you can observe and measure in your garden rather than from dates written for somebody else’s latitude.
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