Valued for showy, four-petaled, silky flowers in bright yellow, pink, or white. Some types display their blossoms during the day, but others open in late afternoon and close the following morning. Flowers of some are fragrant. Plants succeed in tough, rough places. Resist deer.
O. biennis. EVENING PRIMROSE. Annual or biennial. Zones US, MS, LS, CS; USDA 6-9. Variable in size, ranging from 1 ft. to 4 ft. or even as much as 6 ft. tall. Best grown in meadows, as it is usually weedy, reseeds, and can be invasive. Fragrant yellow blossoms open in the evening; they are yellow at first, then fade to gold. Japanese beetles are particularly fond of this species.
O. drummondii. BEACH EVENING PRIMROSE. Perennial. Zones LS, CS, TS; USDA 8-11. Native to the Coastal South and Mexico. Evening-blooming plant that forms a foliage mat 5 in. high and 4 ft. wide; prostrate stems root along the ground, forming offset plants. Narrow, dark green leaves to 212 in. long. Yellow, 212-in. flowers rise on individual stems 68 in. above foliage. Blooms most heavily in spring, sporadically throughout the rest of the year. Endures heat and drought but does better with occasional water.
O. fruticosa. SUNDROPS. Perennial or biennial. Zones US, MS, LS, CS; USDA 6-9. Native to eastern U.S. Erect growth to 2 ft. high and wide. Branching reddish stems are set with medium green, lance-shaped leaves to 412 in. long; leaves turn dull red with frost. From late spring through summer, bears clusters of 1- to 2-in.-wide, deep yellow flowers that open in daytime. 'Fireworks' ('Fyrverkeri') has red flower buds and leaves tinted purplish brown. Foliage of O. f. glauca 'Summer Solstice' ('Sonnenwende') turns bright red in summer, darkens to burgundy in fall. O. f. g. (O. tetragona) has light yellow flowers and red stems; its leaves (red-tinted when young) are broader than those of the species.
O. 'Lemon Drop'. Perennial. Zones US, MS, LS, CS; USDA 6-9. This showy hybrid blooms yellow in the daytime through hot, dry summers, growing 812 in. tall and wide. Use on the front edge of a flower bed, in a mixed container, or as a blooming ground cover.
O. longifolia 'Lemon Sunset'. Perennial. Zones US, MS, LS, CS; USDA 6-9. Grows 24 ft. tall and 13 ft. wide. Fragrant, 4-in. flowers in summer, opening soft yellow in the evening and fading to coral the next day. Can spread underground to form a clump. Tolerates heat and drought.
O. macrocarpa (O. missouriensis). OZARK SUNDROPS. Perennial. Zones US, MS, LS; USDA 6-8. Native to south-central U.S. To 6 in. tall and 2 ft. wide, with narrow, medium green, lance-shaped leaves to 3 in. long. Late spring to early fall, bears pure yellow, 4-in. flowers that remain open all day. Large winged seedpods follow the flowers. Good in rock gardens. Give partial shade in hottest climates. O. m. incana 'Silver Blade' has silvery blue leaves.
O. speciosa. SHOWY EVENING PRIMROSE. Perennial. Zones US, MS, LS, CS, TS; USDA 6-11. Native to southwestern U.S. and Mexico. An old favorite in the South. To 1 ft. high and 3 ft. or more wide, spreading quickly by rhizomes. Forms rosettes of medium green, narrow, 1- to 3-in.-long leaves. Fragrant, 2-in. flowers are white to pinkish, aging to pink; despite plant's common name, they open during the day. Blooms from spring or early summer into fall, then stems die back. Good ground cover for dry slopes or parking strips but is aggressive and invasive. Selections include pure white form 'Alba', light pink 'Rosea', pink 'Siskiyou', and 'Woodside White' (white blossoms with a chartreuse eye).