How to Grow Sweet Fennels | Planting & Establishment

Soil & Growing Conditions

Water: moist but well-drained or well-drained (RHS)

Soil pH range

6 7.5

Span reflects genuine variation between the cited authorities, not a single agreed figure.

Growth Stages

Stage	BBCH	Notes
Sowing	0	Propagate by seed, in full sun on well-drained soil (RHS).
Feathery foliage growth	3	Develops finely divided, feathery, bright green foliage with somewhat swollen leaf bases (RHS).
Flowering	6	Flowers, followed by aniseed-flavoured seed formation; remove faded flowers to prevent unwanted self-seeding (RHS).
Leaf and seed harvest	8	Harvest aromatic leaves and seeds over 1-2 years to maturity (RHS).

Quick Facts

Factor	Value
Soil pH	6 - 7.5
Sunlight	6-6 hours direct sun
Soil texture	chalk, clay, loam or sand (RHS)
Drainage	well-drained
Lifecycle	perennial
Edible parts	leaves, seeds

At a Glance

Harvest & Storage

When to pick: Harvest aromatic leaves and aniseed-flavoured seeds; remove faded flowers to prevent unwanted self-seeding (RHS).

Diseases

Root rot (fennel, causal agent not yet confirmed)

low

RHS names this directly: root rots.

Powdery mildew

low

RHS names this directly: powdery mildews.

Pests

Aphids

low

Aphididae (various spp.)

RHS names this directly: aphids.

Slugs

moderate

Gastropoda (slugs, various spp.)

RHS names this directly: slugs.

Sweet Fennel, RHS's Third Foeniculum Variety

A third, dedicated RHS variety

This candidate's own Wikimedia title names it 'Foeniculum vulgare dulce' directly -- RHS maintains a separate page for this variety alongside Herb Fennel (var. vulgare) and Florence Fennel (var. azoricum).

Somewhat swollen leaf bases

RHS: sweet fennel has somewhat swollen leaf bases, though not as bulbous as traditional Florence fennel -- visible here at the base of this clump.

A vigorous herbaceous perennial

RHS: a vigorous herbaceous perennial reaching 1-1.5m in height and 0.5-1m spread, grown in full sun on well-drained soil.

Grown for aniseed-flavoured seeds

RHS: grown primarily as a culinary herb for its aromatic leaves and aniseed-flavoured seeds, emphasising foliage and seed production over bulb formation.

Aphids, RHS's named pest

RHS names aphids directly as a pest of sweet fennel, alongside slugs.

References

1. RHS (Royal Horticultural Society) - Foeniculum vulgare var. dulce | sweet fennel

   A vigorous herbaceous perennial with finely divided, feathery, bright green foliage and somewhat swollen leaf bases (though not as bulbous as traditional Florence fennel). Grown primarily as a culinary herb for its aromatic leaves and aniseed-flavoured seeds. Not native to GB/Ireland. Hardiness H5 (hardy in most UK locations, even during severe winters). Full sun, tolerates south-, east- or west-facing aspects. Soil: chalk, clay, loam or sand; moist but well-drained or well-drained; acid, alkaline or neutral pH. Height 1-1.5m, spread 0.5-1m. Time to maturity 1-2 years. Propagate by seed. Pests: aphids, slugs. Diseases: root rots, powdery mildews. Foliage and seeds are edible; remove faded flowers to prevent unwanted self-seeding. RHS explicitly distinguishes this variety from both the already-published Herb Fennel (var. vulgare, no swollen leaf base) and Florence Fennel (var. azoricum, a much more pronounced bulb) -- sweet fennel sits between the two, with somewhat swollen leaf bases that are not as bulbous as Florence fennel's.

1 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.