|O.deltoides is an upright annual or perennial with green leaves, lance-shaped to egg-shaped. In summer, single, bowl-shaped white primroses open in the morning then turn to pink at sunset. 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.