The Oenothera is a large genus that contains 145 herbaceous plant species, these can range in height from 15 to 90 cm (6 inches to 3 feet).
They can be annual, biennial, or perennial in nature, but are normally treated as an annual by gardeners.
They bloom for a short period in spring or summer (species dependent) with cup shaped flowers; these can be pink, white or yellow.
Oenothera perennis - Small Sundrops by Gmayfield10.
Some of the common names for Oenothera include Evening Primrose, Sundrops, and Desert Evening Primrose.
Oenothera biennis (Common evening-primrose), photograph by Andreas Rockstein; CC.
Oenothera speciosa (Pink evening primrose), picture by Leonora (Ellie) Enking; CC.
Common Names: Evening Primrose, Suncups, Sundrops, Pink Ladies, White Buttercups.
Life Cycle: Hardy annual. Hardy biennial. Hardy perennial commonly grown as a hardy annual by gardeners.
Height: 4 to 120 inches (10 to 300 cm).
Growing Region: Zones 4 to 9.
The seeds of Evening primrose can be sown outdoors just before the last frost of spring or in autumn in warm areas.
Once sown lightly cover the evening primrose seeds. Oenothera species are able to grow in either partially shaded or sunny parts of the garden.
They are partial to a light soil that is a little sandy and slightly acidic (pH 5.5 to 7).
Oenothera plants can be grown indoors first. They should be germinated in the dark at 18 to 20 degrees centigrade (64 to 68°F), about ten weeks in advance.
Plants should take around one to four weeks to germinate. Once ready transplant into the garden following the last frost. Oenothera should be spaced at 15 cm (small) to 50 cm (large) apart (6 to 20 inches).
Once growing it is fairly easy to take care of Oenothera genus plants.
They should be watered during dry months, and pruned back following flowering to prevent them from producing seeds; as they can take over the garden.
It is best to supply Oenothera with manure in the spring. If you require more plants then they can be propagated by taking cutting in the spring.