Evening Primrose

Oenothera biennis

The common name refers to the habit of the plant to open its flowers only in the evening, and the light yellow color of the flowers is similar to, but should not be confused with the European primrose, Primlua spp.  The Lakota called the plant “ “rattle weed,” and the Potawatomi name was “yellow top.”  The plant forms a rosette and tall flowering stalk, and also should not be confused with other plants with the common name “primrose.”  The medicinal product from this plant this is most common currently is the oil derived from the seed, which is a good source of gamma-linolenic acid, but historically the leaves and roots were also used by Native Americans.

Family:  Evening Primrose/Oenagracea
Life cycle: herbaceous biennial (Zones 3-8)
Native:  Great Plains and eastern North America.  Naturalized throughout most of Europe and parts of Asia.
Height: 2-6 feet.
Sun:  Full sun optimal, will tolerate partial shade.
Soil:  Does best on well drained soil, but will tolerate some wet soils.  Can be grown with low fertility, but will do better with some compost and/or mulch.
Water:   Has low to moderate water requirement.
Flowers:  Bright yellow flowers, 4 petaled, that bloom at dusk each day and fade by midmorning the following day.  Begins blooming in midsummer of the second year of growth usually, but we have observed a few that will bloom in late summer of the first year.
Propagation:  Seeds should be stratified for 3 to 4 weeks to improve germination, then sow directly outdoors, or in seedling flats for transplants.  Seed is extremely small, so controlling the seeding rate would be difficult outdoors.  Seed can also be saved from your own plants, and this plant will reseed.  Space plants at least 12 inches in the row, with 2 to 3 feet between rows.
Pests:  No major pests insect or disease pests were observed in our field trials, though the plants appeared to lack winter hardiness, and/or succumb to root diseases in the second year.
Harvesting:  The flowering tops are clipped when in the early flowering stage. Seed is harvested at full maturity.
Parts used: Seed and/or above ground herb.
Used as:  Oil extracted from seed, herb used as infusion (tea), tincture, syrup.
Medicinal Benefits:   The gamma-linolenic acid in the oil has anti-inflammatory and cell membrane stabilizer activity in the body.  It has been postulated that the oil may be beneficial to neural development in breast-fed infants.  Capsules of Evening Primrose oil have been approved for use in Germany in the treatment of atopic eczema.  Approved in Britain for treatment of atopic eczema, premenstrual syndrome, and prostatitis.  One precaution listed in the PDR is that the oil has the potential to lower the seizure threshold in patients with seizure disorders or those being treated with drugs that lower the seizure threshold.  Native Americans used root tea for obesity, bowel pains, poulticed root for piles, bruises, and was rubbed on muscles to give athletes strength. 
Market Potential: Unknown.  The seed is extracted for oil, but we don’t know if there is a market for U.S. grown seed.  Seed products, but not raw seed was found in the herb catalog sources.  There appears to be a small market for the above ground portion of primrose, with prices ranging from $7.50 to $34.96 per lb dw.
 

KSU Field Trial Data - 2000-2002.

Summary of field trial data: This plant appeared to have few insect or disease pests in its first year of growth, and scored 4.2 vigor rating on a scale of 1-5, and so appeared to be well adapted to Kansas conditions.  A few plants bloomed the first year, which would have produced a seed crop. However, no plants survived in the field at our 3 field test sites to the second year, and a few plants in a demonstration garden survived, but some of those appeared to suffer from a root disease.  We don’t know if our seed source lacked winter hardiness, or if root disease will be problematic for Kansas growers in general.  We did not harvest the crop for seed the first year, and so at this time, we can’t really recommend it as a crop for Kansas.  In future trials, we should see if enough seed is produced in the first year to make this a commercially viable crop.  There appears to be a small market for the above ground portion of primrose, though little information on medicinal use of the herb was found in the literature.