The delicate evening primrose plant is an attractive, ornamental flower that suits a range of planting schemes. Unusually it is a nocturnal plant meaning that its usually yellow flowers remain closed during the day before opening in the evening, attracting moths and other late night pollinators to your garden. Also known as the fever plant, willow herb or tree primrose, the evening primrose plant is equally at home in a meadow as it is in a cottage or coastal garden.
Native to North America, native Americans used the evening primrose plant (Oenothera biennis) to treat wounds and ailments such as eczema. Later the flower was used to treat other issues such as asthma or whooping cough. Today, evening primrose is regularly used in herbal oils to treat various skin disorders and ailments such as rheumatoid arthritis. You can also use the flowers for culinary purposes either cooked or raw in salads and as a garnish.
The attractive flowers of the willow herb typically open as the light fades, providing a rich source of nectar to late night pollinators such as moths.
Flowering profusely throughout the summer, this quick growing flower is sometimes considered invasive. It is also, unfairly, described as a weed. As well as a vigorous growth habit the evening primrose plant also readily set seeds. This means that it quickly spreads through the garden with little effort on your part. However, it is also easy to control.
Despite a vigorous growth habit the flower’s bright yellow blooms make it a popular choice in a range of planting schemes. A vibrant addition to the garden, this is your guide to the evening primrose plant.
Different Varieties of Evening Primrose Plant
The evening primrose is a herbaceous perennial. In favorable growing conditions the flowers can achieve a height of between 3 and 5 ft and a spread of around 2 to 3 ft. Typically producing bright, yellow blooms some cultivars also produce flowers in shades of white and pink.
The most commonly grown variety is the Common Evening Primrose (O. Biennis). This specimen reaches a height of around 6 ft. A biennial flower it is grown for its large, lemon-yellow blooms.
Other cultivars include:
- Large Flowered Evening Primrose (O. Glazioviana), reaching over 4 ft in height this cultivar is prized for its large flowers.
- Small Flowered Evening Primrose (O. Cambrica) can grow to a height of between 1 and 4 ft depending on conditions. As the name suggests this cultivar produces delicate, yellow flowers throughout the summer.
- The Mexican Evening Primrose Plant (O. Berlandieri) is a spreading perennial which rarely exceeds 18 inches in height. It is native to various states including Texas and Oklahoma and Mexico.
- Showy Evening Primrose (O. Speciosa) is a surprisingly hardy cultivar. Both heat and drought tolerant, the plant flowers in shades of white and pale lavender. In favorable conditions it can achieve a height of between 18 and 28 inches.
Typically producing yellow flowers, some cultivars can produce white or pink blooms.
The evening primrose plant is typically grown from seed. You can purchase seeds from garden stores or online seed retailers. You can also collect seeds from wild specimens growing along roadsides or in friend’s gardens.
Growing from Seed
Sow the seeds in their final position either in the fall or early spring. If you are sowing the seeds in the spring, you can begin as soon as the last frost date has passed and the soil is workable. This helps the specimen to establish itself before the summer temperatures begin to warm up. Too much heat early on in the flower’s life cycle may cause it to become leggy or weedlike. You can also start the seeds undercover, in a greenhouse or on a windowsill, before the last frost date, to maximize their growing time before the summer temperatures hit.
Before sowing, prepare the soil and moisten it. This encourages the seeds to stick in place and reduces the chances of them being disturbed by the wind. Sow as thinly as possible before covering with a thin layer of perlite or vermiculite. You can also cover the area with a cloche or row cover to further protect the seeds. This helps to maintain temperature levels around the germinating seeds and seedlings as well as protecting them from various pests. Following germination thin the seedlings out to about 1 ft.
Alternatively, you can sow the seeds undercover in biodegradable peat pots, such as MT Products Peat Seed Starter Pots. Following germination the seedlings still in their biodegradable pots can simply be planted out into the garden. This helps to eliminate the risk of transplant shock.
Fill the pots with fresh, good quality potting soil. Moisten the soil before sowing 2 to 3 seeds per pot. Following germination, pick out the weaker seedlings allowing only the strongest one to grow on. Harden the seedlings off before transplanting, still in the biodegradable pots into their final position.
To transplant, dig a hole large enough to hold the pot. When placed in the hole the top of the root system should sit level with the soil. If you are planting in a site with poorly draining soil, plant so that the top of the root system sits slightly above soil level. Elevating the plant in this way encourages excess water to drain away from the area. Space the transplants out, roughly 1ft apart.
Where to Plant an Evening Primrose
The willow herb is hardy in USDA Zones 4 to 9. Gardeners in cooler climates can either grow willow herb as an annual or in pots, moving the plant to a sheltered position as flowers fade and summer temperatures fall.
Despite flowering only in the evening, willow herb does best in full sun positions. Ideally they should receive 6 to 8 hours of sunlight everyday. These flowers also grow in partial shade positions. Just avoid placing them anywhere overly shady.
Despite flowering as the light fades, these specimens prefer full sun positions.
The soil should be light and well draining. Avoid positions that are wet or poorly draining. This can cause a number of issues such as root rot. A neutral or slightly acidic pH level is ideal. A soil test kit is a great investment if you are unsure of the makeup of your soil.
Before planting work the soil over well, breaking up compacted clumps of soil and removing any weeds and large stones. This is also the ideal time to enrich the soil with a good amount of organic matter such as well rotted manure or homemade compost.
If you are planting in pots, select a large pot with lots of drainage holes. Fill the pot with light, fresh potting soil.
Caring for the Evening Primrose Plant
As the flower’s invasive reputation suggests, the evening primrose thrives with minimal regular care and attention.
While the evening primrose plant can flower throughout the summer, it prefers cooler temperatures. If temperatures become too hot, flowering may slow or temporarily cease. During the summer months apply a thick layer of mulch to the soil around the base of the flower. This helps to keep the root system cool and also improves moisture retention.
Mulching the soil helps to keep flowers cool and flowering during the warm summer months.
When to Water
Aim to keep the soil around the flowers evenly moist. In warmer climates they appreciate a little extra water, particularly on hot days. This helps the root system stay cool and maintains flowering. Flowers in containers may require more frequent watering than those in the ground, particularly during warm periods. Planting in self watering pots is a great way to keep flowers hydrated and flowering in a low maintenance garden.
Browning or discoloration of the foliage is usually a sign that the flowers are sitting in soggy soil. Cease watering immediately. Allow the soil to dry out before watering again. If you are growing in containers, you may need to repot the flowers in better draining soil.
Do I Need to Fertilize my Flowers?
If planted in good or rich soil, fertilizer is not necessary. In poorer soils an occasional dose of a balanced liquid fertilizer can help to stimulate and sustain growth. An effective, healthy liquid fertilizer can easily be made at home.
Whatever the soil condition, the flowers will always benefit from a mulch or top dressing of organic material such as compost or well rotted manure. This is best applied in late spring or early summer.
When to Prune Your Flowers
Deadheading spent flowers helps to prevent the plant from spreading and becoming invasive.
Deadhead and prune the plant back after flowering before seed pods have time to form and ripen. This helps to prevent the evening primrose plant from self-seeding and spreading around the garden. Just after flowering has finished is also the best time to remove any old or crowded stems.
You can also cut back the plant down to about ground level in the fall.
In cooler climates you may need to protect the flowers against severe frosts. Cover the base of the flower with a thick mulch to insulate. This can be removed in early spring, to allow the soil to warm up. You can also cover the plant with a horticultural blanket or fleece jacket.
Flowers growing in containers can simply be moved inside or to a sheltered position in the fall. To make transporting larger pots easier, why not place them on a caddy? The Amagabeli Metal Plant Caddy makes moving even the heaviest pot a surprisingly simple task.
How Long Does it Take for Flowers to Emerge?
In the first year of their life the evening primrose plant won’t flower. Instead a leafy rosette develops at ground level. In year two a tall, stiff flower spike emerges from the rosette. Halfway up the stem secondary branching occurs. The further up the stem you progress, the smaller the foliage gets until, in the summer, flowers form. As the flowers fade seeds emerge.
How to Propagate an Evening Primrose Plant
The evening primrose plant is easily propagated from seeds.
As the flowers fade seed pods emerge. Allow these to ripen on the stem before harvesting. Starting at the tip of the pod, as the pod ripens it turns brown. Once the pod begins to brown you can harvest the pods. Don’t allow them to remain on the stem for too long, this risks the pod splitting and scattering the seeds around the garden.
As flowers fade, seed pods form. Harvest the brown pods before they split to prevent the flower from self seeding around your garden.
Harvest the seeds on a dry, sunny morning. This helps to prevent excess moisture from sticking to the seeds.
Carefully open the pods. Each pod should be packed with small, dark brown seeds. Grainy, green seeds are immature, meaning that you have harvested the pod too early. These won’t germinate and should be discarded.
Store the dry seeds in an airtight jar or paper envelope until you are ready to sow them. Don’t forget to label and date your saved seeds.
How to Identify and Treat Common Problems
Despite the delicate appearance of the evening primrose plant it is a pleasingly robust specimen. Caring correctly for your flowers will help to prevent many common problems.
Growing in well draining soil helps to prevent root rot as well as issues caused by overwatering.
Powdery mildew and leaf spot can be problematic in humid and damp conditions. Spacing the specimens out correctly and cutting away old foliage and stems promotes air circulation around the flowers. This helps to reduce humidity levels, as does keeping the foliage as dry as possible when watering. I find that when watering, a good watering can offers more control than a garden hose.
Regularly check the foliage for signs of infestation. Many different types of beetles like to eat the foliage. However they rarely damage the flower. Mealybugs, aphids, spider mites can also target the foliage and the flowers. An application of neem oil or insecticidal soap can cure most infestations.
Quick to grow and easy to care for, the evening primrose is an attractive addition to any style of ornamental garden.
The evening primrose plant is often unfairly considered by some to be a weed. An attractive flower it is an ideal choice for providing groundcover in sunny positions. Its hardy versatility means that willow herb thrives in a range of conditions and suits a variety of planting schemes including floral meadows, cottage gardens and coastal gardens. It makes a particularly good companion for poppies, dianthus and foxgloves. Wherever you choose to grow your evening primrose plant, remember to control its spread and with just a little care you will enjoy its flowers for many years to come.
Jen is a master gardener, interior designer and home improvement expert. She has completed many home improvement, decor and remodeling projects with her family over the past 10 years on their 4,500 sf Victorian house. She is also a passionate farmer who keeps goats, chickens, turkeys cows and pigs on her farm, and an instructor for her community’s Organic and Sustainable Farming project.