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Fennel (Foeniculum vulgare)

Fennel (Foeniculum vulgare )

Foeniculum vulgare Foeniculum vulgare

Family: Apiaceae, formerly Umbelliferae (carrot, parsley etc)


Robust biennial herb 1 to 2m high with slightly zigzagging stems, which have a bluish bloom. The leaves are finely divided into fine thread-like segments. Flowers are small, yellow and carried in branching umbrella-shaped heads. Fennel smells very strongly of aniseed. The plants die back to the crown over winter, and produce new leaf growth in spring, sending up new flowering stems in summer.

Preferred habitat and impacts:
Usually found on waste ground, such as along roadsides, riverbanks or around the edges of pasture. Grazing may prevent it from becoming established in pasture. Fennel forms very dense infestations, crowding out all other vegetation. While this may not be a problem when it is growing in association with other weeds, it can also affect remnant native vegetation in farming areas.

Fennel is sometimes cultivated for its edible leaf bases, culinary uses as a condiment, and medicinal properties. If cultivating fennel, be careful not to allow the plant to go to seed.

Seed is spread by water, machinery or vehicles, or in contaminated soil, and by wind over short distances.

Another weed in the same family, wild carrot (Daucus carota ) is common on roadsides. It has similar umbrella shaped heads of white or pinkish flowers, and the crushed leaves smell carroty. Hemlock (Conium maculatum ) is another weed in the same family.

A bronze foliaged fennel cultivar is sometimes used for its contrasting foliage colour in cottage gardens. It spreads readily from seed and is difficult to eradicate.

Daucus carota Conium maculatum

Hand chip small infestations (large fennel plants have a very substantial root, so this will be hard work). Slashing just before flowering may kill the plants, or repeat slashing of regrowth may be needed.. At worst, slashing stems at flowering time will prevent seed set and buy a little time before the whole plant needs to be treated, if necessary.

Spot spray actively growing young plants before they elongate into the flowering stage, preferably with a selective woody weed herbicide. If the plants are growing near sensitive vegetation, they can be treated by the cut and paint method, in winter-spring before new growth emerges. Make the cut close to the base or plants will re-sprout. Dense infestations can be slashed or burnt in winter to provide access for spraying in spring.

Wild fennel may sometimes be harvested by people for culinary use, so if spraying in public places, use a dye in the spray, and place a sign indicating that the plants have been sprayed.