Common Fennel
Foeniculum vulgare
Washington State Classification
Class B — Control Required (Designated)
Common fennel escapes cultivation and quickly establishes dense infestations that crowd out native plants that are critical to wildlife habitats.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Common fennel is a large, aromatic, perennial herb. It can grow up to 6.7 feet tall (2 meters) and has a very large taproot. Foliage, stems, roots and seeds are hairless and all have a very strong licorice scent.
Leaves
The leaves have an overall triangular shape and are many times divided into thin, featherlike leaflets and are dark green or bronze. Leaf stems (petioles) are swollen and fleshy and have a widened base.
Flowers
Flowers are small and yellow and form an umbrella shaped cluster. Plants bloom from May to September.
Fruit & Seeds
Seeds are about 0.15 inches (3.5 to 4 mm) long and have small ridges.
Impact
Common fennel escapes cultivation and quickly establishes dense infestations that crowd out native plants that are critical to wildlife habitats. Infestations are becoming more common in Western Washington and may pose a threat to native grasslands.
Ecology & Spread
Habitat
Common fennel can be found along roadsides, in pastures, prairies, streamsides, coastal bluffs as well as wetland areas. Please click here to see a county level distribution map of common fennel in Washington.
Spread Mechanisms
Reproduction
Common fennel reproduces from seed. It can also reproduce from pieces of the root crown.
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Control Methods
Mechanical
- Small infestations can be hand pulled but mature plants are difficult to remove because of the taproot. Above ground growth can be repeatedly cut prior to flowering to deplete below ground energy reserves. This technique may need to be down for several years to be successful. Cutting above ground growth when flowers are present may promote seed dispersal.