The Weed Wire: Fennel
Mature blooming fennel in South Beach
History and Native Range: Foeniculum vulgare 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 by design, as fennel has long been cultivated for culinary usage by many different cultures. Fennel prefers to grow in dry, rocky, disturbed soils, and is often found on seaside bluffs or on road edges.
Identification: 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.
The Problem Here: 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. As such, Lincoln SWCD may be able to offer free chemical treatment for fennel. Please contact info@lincolnswcd.org for help in identification and determining if your property is eligible for this program.
Manual Control: 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.
Herbicides: 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.
Links to Information and Studies:
Eat Your Invasives!
Though the fennel growing invasive in Oregon is not the popular “Florence” or “bulb” fennel- a cultivar grown for its tender, inflated leaf bases- the fronds and fruits of common fennel are still edible and quite flavorful. Use fresh fronds as a garnish for meats and salads, or to make pesto. Dried fronds can be used alone or in a blend to make herbal tea. In many west Asian countries, fennel fruits are chewed as a breath freshener. Give one of these uses a try, and help the environment while you’re at it!
Fennel Frond Pesto:
- 1/2 cup Walnuts
- 1/4 cup Olive Oil
- 1/4 cup Water
- 2-3 cups Fennel Fronds
- 2 Garlic Cloves
- 2 tsp Fresh Lemon Juice
- Sprinkle of Salt to Season
Wash fennel fronds and place all ingredients except walnuts in a blender or food processor. Blend until combined and fronds have broken up into small pieces. Then add the walnuts and blend briefly to combine. If the mixture looks a little thick or dry, add in an extra dash of water or olive oil. Taste and add extra salt if needed, then serve!
Only harvest and consume wild-growing plants from areas you know have not been chemically treated, and for which you have a positive identification.
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