Oenothera is a genus of about 145 species of herbaceous flowering plants native to the Americas. It is the type genus of the family Onagraceae. Common names include Evening Primrose, Suncups, and Sundrops. They are not closely related to the true Primroses (genus Primula).
The species vary in size from small alpine plants up to 4 inches (10 cm) tall, to vigorous lowland species growing up to 10 feet (3 m). The leaves form a basal rosette at ground level and spiral up to the flowering stems. The blades are dentate or deeply lobed. The flowers of many species open in the evening, hence the name "Evening Primrose". They may open in under a minute. Most species have yellow flowers, but some have white, purple, pink, or red. Most native desert species are white. One of the most distinctive features of the flower is the stigma, which has four branches in an X shape.
Growing Conditions and General Care
Oenothera plants can be propagated by dividing established clumps in the spring or in the fall. Softwood cuttings may be struck in late spring. Easy to grow Oenothera seeds can be sown directly in the garden in late summer, early fall, or planted early in the spring.
Just cover the small seeds, and germinate at 65° to 70°F (18° to 21°C). Seeds require darkness to break dormancy. Space plants 5 to 9 inches (13 to 23 cm) apart. Plant in light, well drained soil with a pH of around 5.5 to 7.0. Sandy soil works well for this plant.
Oenothera is tolerant of dry and is a good candidate for xeriscaping. In really fertile soil the foliage can be robust, but fewer flowers form. Top dress with fully composted manure in the spring. Provide irrigation during long hot spells, and cut the plants back by a third after flowering to keep them looking neat. Hot summer weather may cause the plants to briefly stop flowering. Powdery mildew sometimes appears in humid conditions.