|O. glazioviana produces bowl-shaped yellow primroses 2 to 3 inches across, with red-tinged outer calyx, opening in the evening. This upright biennial bears hairy mid-green leaves to 8 inches long; a bit smaller leaves grow on the red-spotted stems. 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.