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Entire healthy mature florence fennel plant in a real garden bed, showing growth habit and scale.Primary identification image. 45–75 cm tall, 30–45 cm wide at maturity.

Florence fennel

Foeniculum vulgare var. azoricum (Mill.) Thell.

Also called: Bulb fennel, Finocchio

Family
Apiaceae
Season
Cool-season annual (herb fennel is perennial)
Best grown in
Portland, Oregon

Grown for its crisp, aniseed "bulb"; bolts readily in spring, so late-summer sowings are more reliable.

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Life cycle & growth stages

  1. 1. SeedSow 1 cm deep in warm soil.
  2. 2. SeedlingEmerges in 7–14 days.
  3. 3. ThinningThin to 25–30 cm.
  4. 4. Bulb swellingStem base thickens; earth up.
  5. 5. Harvest readyBulb 7–10 cm.
  6. 6. HarvestCut at soil level; leave roots for feathery regrowth.
  7. 7. FloweringYellow umbels attract hoverflies if left.

Growth stages are ordered chronologically; timing varies with cultivar, temperature, light and care.

Planting calendar for Portland, Oregon

Start indoors 3–4 weeks before last frost; transplant 1–3 weeks after last frost; direct sow from last frost to 4 weeks after; 65–90 days to maturity from sowing. Windows are derived from the region's average frost dates (last Apr 5, first Nov 5) and are estimates until you confirm your own dates in the calendar.

Florence fennelFoeniculum vulgare var. azoricum
PlantStart indoorsDirect sowAutumn sowTransplantTendHarvest
Florence fennelMar 8–Mar 15 (estimate)Apr 5–May 3 (estimate)Aug 13–Sep 10 (estimate)Apr 12–Apr 26 (estimate)May 3–Jun 9 (estimate)Jun 9–Aug 22 (estimate)
  • Start seeds indoors: Mar 8 – Mar 15
  • Direct sow: Apr 5 – May 3
  • Transplant outdoors: Apr 12 – Apr 26
  • Tend and monitor: May 3 – Jun 9
  • Harvest: Jun 9 – Aug 22
  • Autumn sowing: Aug 13 – Sep 10

Spacing & support

In-row 25–30 cm; rows 45–60 cm. Planner footprint: 1 cell of 30 cm.

Side-profile diagram of mature florence fennel: canopy 45–75 cm tall, 30–45 cm wide, deep root zone, support and harvest-access envelope.

Soil & water

Soil
Fertile, well-drained loam
pH
6–7
Fertility
moderate
Water
Steady water; drought triggers bolting.
Frost
half hardy; tolerates frost

Support & training

No support structure needed.

Florence fennel mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Harvest signs

  • Bulb 7–10 cm across
  • Before a flower stem rises
Florence fennel at harvest readiness, showing the visual cues: bulb 7–10 cm across; before a flower stem rises.

Common problems

Pests: aphids, slugs

Diseases: bolting (physiological)

Appearance alone is not a diagnosis; confirm with a regional extension guide.

Side-by-side: healthy florence fennel leaf or fruit and an example of bolting.

Container growing

  • Minimum 10 L (25 cm deep)
  • Use quality potting mix and water more frequently
Mature florence fennel in a correctly sized container (10 L or more) with drainage visible.

Companion overview

2 reviewed relationship records (evidence: low).

Supported or conditional

None reviewed

Avoid or separate

None with evidence

Traditional claims only: Bush beans, Tomato.

Full companion profile

Crop rotation

Avoid planting florence fennel or other carrot family crops in the same spot for 2 years. Rotation is about previous seasons, not about live neighbours.

Year 1Year 2Year 3ApiaceaeOther familyOther familyback after 2+ years

Shared risks in Apiaceae: carrot rust fly, Alternaria leaf blight, parsley worm (swallowtail caterpillar).

Crop rotation hub

Sources, reviewer & update

Sources

Reviewer: Garden Planner editorial team (pending independent horticultural review)

Last reviewed: August 15, 2026 · version 1

Found an error or have feedback? Let us know.

Growing florence fennel

Florence fennel swells its stem base into a bulb over 65–90 days and is prone to bolting from cold snaps, transplant shock or drought; sowing after midsummer for an autumn crop avoids most of that. Earth up around the bulb as it swells to keep it pale and sweet.

Florence fennel seed beside a ruler or coin for scale.
Florence fennel seedling at cotyledon and first-true-leaf stage, in soil, distinguishable from common weeds.
Florence fennel mid-season before harvest, showing branching, vining, rosette or upright habit and space occupied.

Fennel is widely listed as a "bad companion" that inhibits neighbours. Laboratory studies do find allelopathic compounds in fennel, but the reviewed evidence does not establish a field effect at garden spacing; fennel is tall, deep-rooted and a strong competitor, which explains most of the tradition. Its umbels, if allowed to flower, are attractive to hoverflies and parasitic wasps.

Two or more mature florence fennel plants with a tape measure showing in-row spacing (25–30 cm).
Florence fennel flower detail or bolting stage.
Immature swollen stem base of florence fennel developing on the plant.

Edible parts and safety

Edible: swollen stem base (bulb), leaves, seeds.

Hands or tool harvesting florence fennel correctly (cut, pull, twist or pick) without damaging the plant.

Pests and diseases

Common pests: aphids, slugs. Common diseases: bolting (physiological). These vary by region; a photograph is an example, not a diagnosis. See the pest and disease guides and your local extension service.

aphids on florence fennel, with a wider damage-context view.

Timeline

Season timeline for florence fennel: sowing, transplanting, flowering, harvest and bed occupancy aligned to frost dates.Text alternative: Start seeds indoors Mar 8–Mar 15; Direct sow Apr 5–May 3; Transplant outdoors Apr 12–Apr 26; Tend and monitor May 3–Jun 9; Harvest Jun 9–Aug 22; Autumn sowing Aug 13–Sep 10.

Related plants

See also: Apiaceae family page · crop rotation · regional calendar · guides

Our Methodology & Sources

We synthesize peer-reviewed research, university extension publications, and trusted horticulture resources. Our evidence levels help you understand how strong the science is behind the guidance.

Evidence tiers

Supported evidenceConsistent results from multiple robust studies
Traditional claimHistorical use reported, limited scientific support
Context dependentMixed or variable results across conditions
No verified relationshipNo reliable evidence identified

Primary source types

  • Peer-reviewed journal articles
  • University extension publications
  • Government & research institute reports
  • Systematic reviews & meta-analyses

Last updated

August 24, 2026

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