Evening Primrose


Evening primrose (Oenothera biennis L., Onagraceae) is an erect biennial from a taproot. Its leaves are alternate, lance-shaped and stalkless, the lower ones with red spots and forming a rosette. Flowers are yellow with 4 petals, in a spike at the ends of the stalks, and open widest at night or on dark, overcast days. Seeds are contained in long capsules. Plants germinate and make a taproot the first season, then flower the second season. They are self-fertilizing.

History And Use

Seeds of evening primrose have been used as a substitute for poppy seeds, while the roots and leaves have been used as a vegetable. Roots have also been used as a treatment for hemorrhoids, and the leaves as a poultice for skin eruptions. Evening primrose seed oil has a high gamma-linolenic acid (GLA) content, and is used today in treating eczema, migraines, arthritis, diabetes, benign breast disease, high blood pressure, PMS symptoms, and as a dietary supplement.

Area Of Adaptation

Evening primrose is a common species in disturbed areas and waste places, where the soil is sandy or gravelly and of low quality. High levels of nitrogen may result in lower GLA content. It prefers full sun or partial shade. When cultivated, a fertile loam with pH 5.5 - 8.0 and good drainage is best. Its natural distribution area includes the southern half of Canada (as far north as Gillam in MB) and the adjacent US, extending down into Texas and Florida.

Cultivation And Processing

Evening primrose requires light for germination, so should be scattered on the soil surface and tamped lightly. Watering and freezing the seeds may help in germination by cracking the seed coats. Fields must be kept weed-free, as extractors want 98 percent purity. Fusilade II has been registered for control of grassy weeds, others must be mechanically weeded. Harvest when most of the capsules are mature, but before the seeds have started to shatter. It may be straight combined or swathed first. The oil is extracted from the crushed seed for use.


Evening primrose was over produced in China in the late 1980's, which led to the disappearance of the market. The market today is still very uncertain, making it a high risk crop. The 1997 price for evening primrose oil was US$1.00/lb. Some evening primrose oil products are registered as nutritional supplements with Health Canada.