Oenothera is a genus of the Onograceae family that contains over 125 species of flowering plants. The majority of the plants in this genus are native to North America, but there are also some species found on mountain slopes and deserts in South America. Oenothera plants are known for their large, four-petaled flowers that open and close in symmetry with dawn and dusk. Many Oenothera species are grown as ornamental plants, such as evening-primrose, suncups and sundrops.
Ornamental Oenotheras are cultivated for their striking flowers that continue to blossom throughout the summer. An Oenothera flower consists of eight stamens and four petals that curve inwards toward the middle of the flower at their tips. Most Oenothera flowers are bright yellow and resemble a large buttercup. These flowers are formed in shapes resembling cups, bowls and, occasionally, trumpets.
The Oenothera genus is fairly diverse in terms of the various life cycles of its plants. There are species of wild and commercial Oenotheras that are annuals, perennials and biennials. Annuals go through their an entire life cycle within a single year, while perennials continue to live from one growing season to the next. Biennials, on the other hand, take two years to complete a life cycle.
Three of the best Oenotheras to plant in a garden are O. macrocarpa, O. acaulis and O. agrillicola. O. macrocarpa is a hardy, fast growing perennial with attractive lance-shaped leaves and golden yellow flowers that are 5 inches (about 13 centimeters) in diameter. Evening-primroses like the O. acaulis have attractive flowers that open during the sunset with trumpet-shaped flowers. O. agrillicola is a biennial from the Appalachian Mountains that is a perfect rock garden plant.
The propagation method used for Oenotheras is dependent on the species' life cycle. Annuals and perennials can be propagated by seed during the early spring or late autumn. Biennials should be seeded during the early autumn. Oenotheras can also be propagated by dividing existing plants. Some Oenothera species propagate vigorously on their own and can become invasive if they are not controlled.
Nearly all of the species are very easy to grow and can establish themselves on their own if they are planted in the right conditions. Most Oenothera species thrive in poor or lightly fertilized soil. The roots systems of Oenotheras prefer plenty of stones to cling to and a considerable amount of drainage. These plants should be planted in full sun and should not be over-watered.