Common evening-primrose is an herbaceous perennial plant recognized by its yellow flowers, which open in the evening and close again at sunrise. It is often cultivated as a decorative plant, especially in drought-prone areas. Native Americans cooked Oenothera biennis roots as a food source, but it is said that consumption of this plant could cause headaches and diarrhea.
I. Appearance and Characteristics
Oenothera biennis, the common evening-primrose, is a species of flowering plant in the family Onagraceae, native to eastern and central North America, from Newfoundland west to Alberta, southeast to Florida, and southwest to Texas, and widely naturalized elsewhere in temperate and subtropical regions. Evening primrose oil is produced from the plant.
Other common names include evening star, sundrop, weedy evening primrose, German rampion, hogweed, King’s cure-all and fever-plant.
Oenothera biennis usually has a life span of two years (biennial) growing to 1.6 m (5 ft 3 in) tall in the seeding year. The leaves are lanceolate, 8–18 cm (3–7 in) long and 2–6 cm (3⁄4–2+1⁄4 in) wide, produced in a tight rosette the first year, and spirally on a stem the second year. However, plants with annual life cycles are documented, and have been selected for under experimental conditions in environments with low competition.
- Growing Cycle
Most commonly, O. biennis grows as a low, spreading herb in the first year, just a few centimeters tall, with its leaves spreading out in a rosette to cover the ground, whilst storing energy in a thick root. In the second year, it grows up much taller, to around 1.6M tall, on a semi-woody stem, which then flowers and seeds. This will usually die at first frosts, but occasionally grows another stem in the third year.
- Blooming and Fruiting
Blooming lasts from late spring to late summer. The flowers are hermaphrodite, produced on a tall spike and only last until the following noon. They open visibly fast every evening producing an interesting spectacle, hence the name “evening primrose”.
The blooms are yellow, 2.5–5 cm (1–2 in) diameter, with four bilobed petals. The flower structure has a bright nectar guide pattern, invisible to the naked eye. This pattern is apparent under ultraviolet light and visible to its pollinators, moths, butterflies, and bees.
The fruit is a capsule 2–4 cm (3⁄4–1+1⁄2 in) long and 4–6 mm (0.16–0.24 in) broad, containing numerous 1–2 mm (0.04–0.08 in) long seeds, released when the capsule splits into four sections at maturity.
This plant is a weedy species that favors disturbed environments. It has been introduced and established on all continents except Antarctica.
The seeds of the plant are important food for birds, including American goldfinch, Northern bobwhite, and mourning dove, and it is a larval host for both the primrose moth and the white-lined sphinx moth. Bumblebees and honeybees also visit the flowers.
The seeds of O. biennis can remain viable in the soil seed bank for 70 years or more.
II. How to Grow and Care
Sunlight
Contrary to what you may believe about a plant that only blooms at night (making it perfect for moon gardens), evening primrose actually loves sunlight. It should be grown in a spot that gets full sunlight (or partial shade) and somewhere that the plant can soak in at least six to eight hours of warm sunlight daily.
Temperature and Humidity
While it blooms and grows best during late summer, evening primrose actually prefers to be cool rather than warm. The plant needs to get established with roots and foliage during the cooler early months of spring to flower welcome summer. Too much heat early on in its life can cause the plant to become leggy or resemble a weed in appearance.
Watering
Common evening-primrose does not require a large amount of water, so water frequently but not heavily. Often, rainfall is enough for these plants. Seedlings will need to be watered more often.
Soil
Another major requirement for growing evening primrose successfully is soil that boasts good drainage. That being said, the soil should still retain moisture, just not become water-logged. Consider adding a thick layer of mulch atop the soil to help keep the roots cool throughout the summer. Evening primrose can grow well even in rocky, sandy soil.
Fertilizing
Common evening-primrose will benefit from liberal fertilization. In some cases, it is not needed at all. Soil that is enriched with organic matter is best, so consider applying manure prior to planting. Plants have been reported to thrive on a peat-based substrate.
How to Grow from Seed
Evening primrose is typically grown from seed and, although you can buy the seeds online, you can just as easily collect seeds from large colonies of wild plants growing along the roadside. (Always use caution when foraging along roadways and ensure that you are not trespassing.) Once you get evening primrose seeds, directly sow them in autumn in a location that boasts full sun where the soil has been previously cultivated. Sow the seeds on top of the soil and water well.
After germination, thin the seedlings so that they are approximately 1 foot apart. The seeds need a cold period, called stratification, in order to germinate. If you sow seeds indoors, use a small container filled with moistened seed-starting mix, sow the seeds on top of the soil, cover, and place in the refrigerator to mimic a natural chilling period. Take out in late winter to pot up the plants when they have two sets of true leaves.
In its first year of life, evening primrose will not flower but will simply produce a leafy rosette at ground level. During the second year, a tall, stiff flower stem shoots up out of this base. About midway up this flower stem, secondary branching occurs, and the leaves become progressively smaller the farther you go up the flower stem. The four-petaled blooms that begin emerging at the start of summer are about 1 inch wide. They’ll eventually die off and produce seeds, which are then spread throughout the landscape by various weather conditions or eaten by wild birds.
Pests and Diseases
Common Pests
Varieties of beetles eat the leaves of evening primrose, but they won’t do enough damage to kill the plant. Otherwise, you can expect to see various other traditional garden pests periodically, including leafhoppers, lygus bugs, and aphids.
If you notice signs of infection on your plants, treat them with insecticidal soap or a diluted oil such as neem oil.
Common Problems
Though evening primrose is a rather easy plant to grow and manage, it will sometimes show a few problems.
- Decaying or Wilting
This is often the result of bacterial soft rot, which occurs at temperatures between 70 and 80 degrees Fahrenheit and affects plants that are sitting in soggy soil or very humid conditions.
- Yellowing Foliage and/or Stunted Flowers
Fungal diseases are known to limit the plant’s ability to take up water and nutrients, leading to yellowing of the leaves, stunted flowers, and root rot. Pull these flowers up and discard them to prevent the fungus from moving to other plants.
- Discoloration of Foliage and Flowers
This can be caused by gray mold, which can cover the plant with fuzzy gray and brown spots. This happens even as the plant slowly succumbs to the resulting lack of nutrients. Pull the plants to prevent the spread.
III. Uses and Benefits
- Ornamental uses
The upright growth and unusual leaves of common evening-primrose (Oenothera biennis) make for a diverting garden feature plant. The plant really comes into its own in summer and fall when its bright yellow flowers bloom, attracting butterflies, bees, and hummingbirds. Common evening-primrose is suitable for beds and borders in cottage and informal gardens and is particularly attractive in combination with poppy, sage, and garden catchfly.
- Medicinal uses
Beyond being a beautiful, vibrant addition to your garden or landscape, evening primrose plants have a storied history in the medicinal community; some of the common names for the plant, such as cure-all or fever plant, allude to these holistic properties. These days, it’s most commonly seen as an herbal supplement or oil and used for skin disorders, as well as pain issues related to diseases like multiple sclerosis and rheumatoid arthritis
- Culinary uses
Most of the plant parts are edible, having a taste that is mild. The roots can be eaten raw or cooked like potatoes. The leaves can be eaten raw in salads or cooked like spinach or in soups. Anishinaabe tribes traditionally make tea from the evening primrose leaves for use as a dietary aid and to reduce fatigue.
The flowering stems are preferably used when they are still young in June. They have to be peeled and can then be eaten raw or fried. The flower buds are regarded as a delicacy and can be harvested from June to October.
The seeds have a protein content of about 15%, an oil content of 24%, and contain about 43% cellulose. The proteins are especially rich in the sulphur-containing amino acids, methionine and cysteine, and tryptophan. Gamma-linolenic acid (GLA), and linoleic acid are present. Mainly for these polyunsaturated fatty acids, evening primrose oil is sold as a dietary supplement.
