How to grow fennel (bulb)
Foeniculum vulgare var. azoricum · Apiaceae · Vegetable
When to plant fennel (bulb): the short answer
Start seeds indoors about 4 weeks before your last spring frost; plant out about 1 week before it; sow outdoors about 1 week before the last frost; for a fall crop, sow about 12 weeks before your first fall frost. Seeds germinate in soil from 60 to 80°F, fastest near 70°F.
Cold winters (zone 5): plant out Apr 16 – May 3, or sow Jul 3 – Jul 20 for a fall crop. Mild winters (zone 9): sow Aug 28 – Sep 14 for fall and winter harvests; the spring window (Feb 6 – Feb 23) closes before the summer heat. Skip the hottest months for fennel (bulb). See every zone.
Fennel (Bulb) is a cool-season vegetable in the Apiaceae family, grown either from a direct sowing or from transplants. It wants full sun (six or more hours of direct light) and steady, even moisture. From sowing to first pick is about 65–90 days. It shrugs off a light frost but a hard freeze will damage it.
Grower’s note: Bulb (Florence) fennel bolts in heat and after a cold snap, so the fall crop is far more dependable. Hill soil around the swelling base to blanch it. It hinders many neighbours - keep it in its own corner, away from dill and coriander (they also cross-pollinate).
Sowing
Sow about 0.25″ deep, into soil between 60–80°F — germination is quickest near 70°F. Germination takes a week or two (7–14 days). For an early crop, start seed indoors about 4 weeks before your last spring frost and grow it under bright light.
Spacing & layout
Give each plant about 8″ along the row with roughly 18″ between rows. On a square-foot grid that is 4 per square foot. Allow at least 12″ of loose, workable soil for the roots. It grows well in containers at least 12″ deep.
Fitting it to your season
As a cool-season crop, fennel (bulb) does its best growing in the mild weather of spring and fall and tends to bolt or turn bitter in summer heat. A second sowing in late summer, timed to mature as the weather cools, is usually the better crop of the year — though a hard freeze will end it.
Quick facts
Growth stages: how long fennel (bulb) takes to grow
From sowing to first harvest takes roughly 65-90 days (9-13 weeks), with seedlings appearing after 7-14 days in soil around 70°F.
When to plant fennel (bulb)
When to plant fennel (bulb) by USDA zone
Dates worked out from each zone’s typical frost dates for 2026. Find your zone on the zone map, or pick your state below for dates from its own frost dates. Zones 11 and above are frost-free, so timing there depends on heat and rain instead.
| Zone | Last / first frost | Start indoors | Sow or plant out | Fall or second sowing |
|---|---|---|---|---|
| Zone 3 | May 15 / Sep 15 | Apr 10 – Apr 24 | May 1 – May 18 | Jun 13 – Jun 30 |
| Zone 4 | May 10 / Sep 25 | Apr 5 – Apr 19 | Apr 26 – May 13 | Jun 23 – Jul 10 |
| Zone 5 | Apr 30 / Oct 5 | Mar 26 – Apr 9 | Apr 16 – May 3 | Jul 3 – Jul 20 |
| Zone 6 | Apr 15 / Oct 15 | Mar 11 – Mar 25 | Apr 1 – Apr 18 | Jul 13 – Jul 30 |
| Zone 7 | Apr 5 / Oct 25 | Mar 1 – Mar 15 | Mar 22 – Apr 8 | Jul 23 – Aug 9 |
| Zone 8 | Mar 20 / Nov 5 | Feb 13 – Feb 27 | Mar 6 – Mar 23 | Aug 3 – Aug 20 |
| Zone 9 | Feb 20 / Nov 30 | Jan 16 – Jan 30 | Feb 6 – Feb 23 | Aug 28 – Sep 14 |
| Zone 10 | Jan 30 / Dec 15 | Dec 26 – Jan 9 | Jan 16 – Feb 2 | Sep 12 – Sep 29 |
Companions
No strong companions recorded.
Dill, Cilantro / Coriander, Tomato, Bush Bean, Pole Bean
Common problems
Pests: black swallowtail caterpillar, aphids.
Diseases & disorders: cercospora leaf spot, root rot.
Same family (Apiaceae)
Rotate these so they don’t follow each other in the same bed year to year.
Questions gardeners ask
When should I plant fennel (bulb)?
Start seeds indoors about 4 weeks before your last spring frost; plant out about 1 week before it; sow outdoors about 1 week before the last frost; for a fall crop, sow about 12 weeks before your first fall frost. Seeds germinate in soil from 60 to 80°F. The table on this page gives dates for each USDA zone, and the planting calendar gives dates for your own state or ZIP code.
How long does fennel (bulb) take to grow?
About 65-90 days from sowing to the first harvest. Seeds germinate in 7-14 days, fastest in soil around 70°F.
How much sun does fennel (bulb) need?
It needs at least six to eight hours of direct sun a day.
What soil pH does fennel (bulb) need?
A soil pH between 6.0 and 7.5. Test before adding lime or sulfur - see the soil pH and testing guide.
How far apart should I plant fennel (bulb)?
Space plants about 8 inches apart in rows 18 inches apart, or 4 per square foot in a square-foot bed. Sow seeds about ¼ inch deep.
Can I grow fennel (bulb) in a container?
Yes. Use a container at least 12 inches deep with drainage holes and a good potting mix, and water more often than you would in the ground.
Figures are typical home-garden ranges from Cooperative Extension planting guides, cross-checked against multiple state sources. Your variety and conditions will vary.