With such a location-specific name, the Missouri primrose (Oenothera macrocarpa) might make the perfect official state flower, but Missouri's happens to the be hawthorn blossoms. Nonetheless, this perennial bears lots of lemony yellow flowers across summertime, opening in the late afternoon as dusk approaches. Grow it throughout U.S. Department of Agriculture Hardiness Zones 5 through 8.
The natural range for the Missouri primrose, or Missouri evening primrose, extends from southeastern Nebraska and Missouri southward to east-central Texas and over to Tennessee. This wildflower has become naturalized in an even larger land area in the southern and central United States today.
A member of the willowherb or evening primrose family, Onagraceae, the currently accepted botanical name is Oenothera macrocarpa although older literature still lists the old synonym of Oenothera missouriensis. This wildflower has many alternative common names, including Ozark sundrop, fluttermill and big-fruit evening primrose. Confusingly, any yellow-flowering species of evening primrose may casually be called a Missouri evening primrose by an inexperienced gardener since there are many primrose species native to the United States.
Missouri primrose grows about six to 12 inches tall in an upright clump or more sprawling habit with thin and short lance-like leaves. The gray-green leaves attach to a red-blushed stem. In summer, among the leaves at the tips of stems occur large, lightly fragrant yellow flowers. The four-petaled blooms open in late afternoon and remain open overnight, closing the next morning. While short-lived, the abundance of flower buds over several weeks and the colorful stems creates an attractive display. The winged seed pod ripens to release many seeds. Frosts kill the plant back to the roots or lowest stems.
Sow seeds of Missouri primrose either in autumn or spring in any well-draining soil that isn't too fertile. It naturally grows in sunny loam-soiled meadows or rocky hillsides; avoid clay soils. Gravelly soils and those that are alkaline support this wildflower well as long as they never become soggy or bone dry. Plant it where it receives at least six hours of direct sun daily. When established, a plant will shed seeds naturally and more plants will sprout and expand the primrose display year after year. Consider removing old spent flowers in formal garden settings for tidiest appearance and longer flowering season.
Scatter seeds in a short-grass meadow and allow to naturalize and attract moths and bees to the garden. It makes a nice clumping accent in a moist rockery or clustered or lined as an edging in the front of a mixed perennial border. It does not make a good cut flower.