How to Grow Fennel
Fennel At a Glance
Difficulty
Moderate
Category
Vegetable
Sun Exposure
Full Sun, Partial Sun
Frost Tolerance
Frost Tender
Cold Hardiness
Survives to -7°C
Plant Family
Apiaceae
Growing Season
Cool & Warm Season
Plant Lifecycle
Annual
How to Start It
★ Recommended for beginners
Fennel dislikes cold and being moved, so sow it right where it will grow once the soil is warm, about 4 weeks after your last spring frost. Sow 2 to 3 seeds 1 cm deep every 20 cm and cover them. They sprout in 7 to 14 days: keep the strongest seedling at each spot.
This guide is for bulb fennel (Florence fennel), grown for its sweet, crunchy, anise-flavoured base. Anything that stresses it, like cold nights, dry soil or a disturbed root, can make it bolt (rush to flower) before the bulb swells, so steady care matters most. The feathery leaves and the seeds are tasty too.
When To Start
First chance to plant
7 Days After Last Frost
Last chance to plant
60 Days Before First Frost
When should you plant Fennel?
Your planting dates depend on your local climate. Sign up and add your location to unlock personalized dates.
Your Fennel Planting Window
Start planting
May 15, 2026
Last chance
Sep 10, 2026
Your Fennel Calendar
Set your location to turn these into exact dates and reminders.
Sow fennel outdoors now, where it will grow
30 days after your last frost· every year
Optional: start fennel indoors in small cells
1 week before your last frost· every year· optional
Cut fennel bulbs when firm and the size of a tennis ball
110 days after your last frost· every year· optional
Did you water your fennel seedlings today? Keep the top of the soil damp until they are up and growing.
About 1 days after you plant it
How is your fennel coming along? Keep the soil evenly moist, since dry spells can make it bolt to flower.
About 44 days after you plant it
Almost there! Pull a little soil up around the base to keep the bulb pale and tender.
About 74 days after you plant it
Picking time may be here: check your fennel.
About 90 days after you plant it
The Journey Ahead
Fennel's Lifecycle
Seedling
Mature Plant
Seed Production
Step 1
Prepare Your Space
1 cm
Seeding Depth
20 cm
Plant Spacing
45 cm
Row Spacing
1
Plants / Sq Ft
Vertical Growing
Yes: Trellis.
Method: Trellis.
Succession Planting
Yes.
Step 2
Planting & Sprouting
Expect sprouts in 7–14 days
Growing Tips
- 1Grow fennel in full sun, at least 6 hours a day.
- 2Mix plenty of compost into the soil, since fennel needs rich soil to make a big bulb.
- 3Water deeply about once a week so the soil never dries out, and mulch to keep it evenly moist.
- 4Feed with worm castings or compost tea every 3 to 4 weeks once the bulb starts to swell.
- 5When the bulb is the size of an egg, pile soil around it to keep it pale and sweet.
- 6Wash aphids off with a spray of water, and move any green, black-striped caterpillars (future swallowtail butterflies) by hand to a spare plant.
Seedling Phase
Step 3
Growth & Maturity
~90
Days to Maturity
150 cm
Mature Height
45 cm
Mature Width
Pests to Watch For
Diseases to Watch For
Mature Plant
Step 4
Harvesting
Harvest Window
30 days
When to Pick
Harvest bulb and fronds when mature
How to Harvest
- 1Harvest the bulb when it is firm and about the size of a tennis ball, usually about 90 days after sowing.
- 2Cut it at the base, just above the soil, with a sharp knife.
- 3Leave the root in the ground, and small tender shoots often grow back for a second, smaller picking.
- 4Snip a few of the feathery leaves any time to use like dill in salads and fish dishes.
- 5Cut off the stalks and keep the bulb in a bag in the fridge for about a week.
- 6Any plant that bolts still gives you fennel seed for cooking once the flower heads turn brown.
Step 5
Saving Seeds
How to Save Seeds
Fennel seeds come true if the variety is not a hybrid (hybrid F1 seeds will not). Bulb fennel and the herb fennel grown for leaves cross easily through insects, so let only one kind flower within about 800 m. Leave a few strong plants to flower, and cut the flat seed heads when the seeds turn from green to grey-brown. Dry the heads in a paper bag for a week or two, then rub the seeds loose. Store them labelled in a cool, dark, dry place, where they keep about 4 years.
Seed Production
Still have a question?
Ask your coach about your fennel.
This page covers what we thought to write down. Your fennel will do something it never mentions, and that is the day a coach beats a guide. Ask Coach Lumen one question right now, free, no account.
