Oenothera biennis, a hardy biennial, provides a wonderful splash of summer colour in the garden. Flowering begins in June and plants continue growing throughout the season so there is a constant succession until about September. Commonly known as Evening Primrose, in early summer the sweetly scented, bright yellow flowers open towards evening and are faintly phosphorescent. This introduced and widespread naturalised, although apparently decreasing wild flower, has a bright nectar guide pattern, invisible in visible light, but apparent under ultraviolet light, which assists pollination by moths, butterflies and bees. The fragrant flowers are mostly fertilised by twilight-flying pollinating insects, along with moths and bats. Later in the season the flowers open all day but not have a scent until the evening. The seeds are also a good food source for birds.
