|O. biennis is an upright annual or sometimes a biennial, producing fragrant pale yellow primroses turning darker in the evening. Large rosettes, slightly sticky are lance shaped to oblong. Best planted in spring among other full sun plants. You should divide the clumps every 3 years to encourage them to flower. Evening Primroses are excellent perennials for weekend gardeners, since they are simple to grow, with almost no pests or problems.