What is Fennel?
Fennel is a large, aromatic perennial herb in the carrot family, which originates from the shores of the Mediterranean Sea but is now found on all continents but Antarctica- it is especially prevalent in coastal areas. Much of this global dispersion is a result of its longstanding cultivation for culinary purposes. Fennel prefers to grow in dry, rocky, disturbed soils, and is often found on seaside bluffs or on road edges.
Physical Description
Fennel can easily be spotted during the late summer and early fall by its umbels of yellow flowers, growing atop hollow, greyish-green, segmented stems which can reach up to seven feet tall. The leaves are thin, threadlike, and finely branching; somewhat resembling dill. The yellow flower umbels and threadlike leaf fronds allow fennel to easily be distinguished from species such as cow parsnip, poison and water hemlock, and Queen Anne’s lace, which have white flower umbels and flat leaves. Additionally, fennel leaves have a strong licorice-like scent when crushed, unlike other plants found locally.
Why is Fennel a Problem?
With its hardy growing capabilities and prolific seed production, fennel can easily escape cultivation and disperse into the natural landscape. It can also regrow from root crown fragments, opening the possibility for introduction from fill dirt. Fennel is a prolific weed throughout most of coastal California, and in some places may be the most dominant plant species on the landscape. It is suspected that fennel produces chemicals that inhibit plants of other species from easily growing alongside it. Left uncontrolled, fennel may take over entire meadows and hillsides, edging out sensitive native flora and the fauna that depend on them.
As changing climates bring warmer and drier weather to the Oregon Coast, growing conditions for fennel are becoming more and more favorable. Recent years have seen a northward migration of the plant up from California, though populations have not yet reached the sizes and densities often seen further south. In order to get ahead of this looming issue, fennel has recently been designated as a high-priority species in our Early Detection, Rapid Response (EDRR) program. Please contact info@lincolnswcd.org for help in identification and determining if your property is eligible for this program.
Controlling Fennel
Mowing or slashing fennel before it flowers can help control infestations by preventing seed production and depleting the plant’s energy, but will not eliminate infestations as the plant will almost always regrow. Digging out the root crown will prevent regrowth, but this may be difficult or impossible due to fennel often growing in rocky soil or cracks between pavement.
Chemical control is generally considered the most effective measure for controlling fennel infestations, with foliar applications of triclopyr and/or glyphosate showing best results. Chemical applications are best done before the plant has flowered, and should always be carried out according to label directions.
More information on fennel and its control can be found here: