Fennel

Grown for its feathery foliage and aniseed flavour, not to be confused with Florence fennel's edible bulb. A tall, hardy perennial that self-seeds freely and is a magnet for beneficial insects once it flowers.

Written by Yemi · Last reviewed August 2026

Maturing this month

First sprouts in 10-14 days at soil temperatures above 10°C

Difficulty

Fennel should be ready to harvest this month. Check for size and colour.

Growing Calendar

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Sow

Transplant

Harvest

This month: Sep

Log to journal

Ready to harvest now

•Check size and ripeness
•Harvest regularly
•Store or use fresh

Sowing Guide

What you'd find on the seed packet

Sow Depth

1cm

Spacing

45cm

Germination

10-14days at soil temperatures above 10°C

Thinning

Thin to 45cm apart once seedlings have two true leaves

Grower's Note

Sow direct where it's to grow rather than starting in modules, fennel has a taproot and resents being transplanted.

Recommended Varieties

Bronze fennel ('Purpureum') has striking dark bronze-purple foliage and is equally hardy, chosen mainly for ornamental value alongside the plain green form.

Planting Out Guide

Best spaces, conditions and how to plant out

Plant Spacing

45cm, more if grown for its architectural height

Best Grown In

Open ground away from other vegetables it may compete with, a herb border, or a wilder corner

Conditions

Full sun. Moist but well-drained, fertile soil.

Grower's Note

Give it real distance from dill (they cross-pollinate) and from smaller vegetables it can overshadow or outcompete once established.

Growing Stages

Approximate weeks from sowing to harvest

Sprouting

2wks

Seeds germinate and first leaves emerge. Keep warm and moist.

Establishing

6wks

Root system develops and plant builds structure. Pot on if needed.

Maturing

12wks

Plant reaches full size and begins producing. Harvest at peak.

Total~20 weeksfrom seed to harvest

Companion Plants

Plant these nearby for natural pest control, better yields, and healthier soil.

Broccoli

Attracts Pollinators

Left to flower at a distance, fennel's umbels draw in hoverflies and parasitic wasps that help control aphids on nearby brassicas. Give it real space though, closer planting can suppress the growth of many vegetables.

Cucumber

Attracts Pollinators

Its flowers are a strong late-summer draw for pollinators and hoverflies, useful near cucumber if kept at a distance rather than directly interplanted.

Climate Control

Today

—C

Humidity

—%

Water

Every 2–3 days

Sunlight

6+ hours direct sun

Watch Out For

Self-seeds very readily once established: deadhead spent flowers if you don't want seedlings appearing throughout the bed

Grown too close to dill, the two will cross-pollinate and both can lose their true flavour and seed viability: keep them well apart

Slugs can strip young seedlings before they establish: protect with a barrier or nematodes until plants are a few centimetres tall

What You'll Need

Equipment for growing fennel

Modular Seed Tray

96-cell for precision sowing

Fine Rose Watering Can

Gentle shower for seedlings

Bamboo Canes

Pack of 20 × 120cm

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Grown Organically

Every method in this guide works with natural systems: no synthetic chemicals, no shortcuts.

Read our approach

Common Questions

About growing Fennel in the UK

What's the difference between fennel and Florence fennel?

They're the same species, grown differently. Herb fennel (this entry) is grown for its feathery leaves and aniseed-flavoured seeds. Florence fennel is grown for its swollen, edible bulb-like stem base, and needs a different growing approach entirely, see the separate Florence Fennel guide.

Why is my fennel taking over the garden?

Fennel self-seeds very readily once established. Deadhead flowerheads before they set seed if you want to keep it contained, or accept the odd seedling and remove unwanted ones while small.

Can I grow fennel and dill together?

It's best avoided. Fennel and dill cross-pollinate if grown near each other, which can affect the flavour and seed-saving reliability of both. Keep them at opposite ends of the garden if you're growing both.

Does fennel come back every year?

Yes, herb fennel is a hardy perennial in most of the UK. Top growth dies back after the first frosts and resprouts from the base the following spring.

Written from real growing experience, not just research. Read the story behind Pelham Gardens.

Member guides

There's more to growing Fennel than this guide covers.

A Garden Journal to log what worked, a personalised sowing planner in My Garden, and monthly reminders timed to the calendar.

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