|O.missouriensis is a perennial with trailing stems in a red-tinted color, branching from a central rootstock. Leaves are egg-shaped in a pale to mid green. Bright yellow primroses in a cup shape, to 5 inches across with red flecked calyces. These beautiful flowers open in the evening and remain open in the day hours from May to August. 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.