|O.caespitosa are clump-forming biennials or perrenials with spoon-shaped, entire toothed, gray-green leaves. Cup-shaped white primroses open at sunset, turning pink with age. 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.