Fennel (Foeniculum vulgare Mill.) is a perennial herb that is native to the Mediterranean and southern Europe. While it is cultivated as a perennial in warmer climates, it must be grown as an annual in Montana. Two kinds of fennel are available: the finocchio or Florence fennel forms thickened leaf bases and is used as a vegetable. The leaf and seed type does not form thickened leaf bases, and may be classified as bitter (var. vulgare) or sweet (var. dulce) (3). Fennel seed is used as a flavoring for foods and beverages, and the essential oil from the seed and plant has flavoring, cosmetic, and pharmaceutical uses. 

Fennel oil may be used directly as a flavoring or given further treatment to produce anethole for the beverage industry. China and Vietnam are major producers of anethole from another plant, the star anise, and are supplying a large proportion of the demand.

 Fennel may be grown by direct seeding or from transplants, but a long growing season is required to mature the seeds. Flowering is initiated when day length reaches 13.5 hours. Our 1998 harvest date of October 5 was after the Bitterroot Valley’s normal mid-September first frost date. Seed maturity was achieved in 1998, but in the normal growing season of 1999, fennel was harvested when seeds were immature and the entire plant distilled.

 Oil may be steam-distilled from the seeds or from the flowering top. Direct heading may be done to harvest mainly the oil-rich seed heads. At the WARC, mature fennel plant tops or crushed seeds were distilled after air drying in 1998, and plant tops with immature seeds were distilled without drying in 1999.


Fennel can be grown in the Bitterroot Valley’s short growing season if the plants are harvested with immature seeds and distilled without drying. The seeding rate was reduced from 6 to 3 lb/a in 1999, and the lower rate resulted in a similar biomass with a lower plant stand. 

Oil production from the plant tops was acceptable, as aboveground parts normally contain

1-1.5% oil (3). The anethole content of the herb oil exceeded the standard of 50-60% (2). Conversely, fenchone was less than 5%, above which the oil has a bitter flavor (1). Limonene levels were high in both years of the study, but sweet fennel oil can contain as much as 30% limonene. The market for fennel oil is limited because of the prevalence of alternative sources of anethole, and because wild fennel is harvested for oil in many parts of the world.

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