Four o'clocks are leafy, shrublike, multi-branched perennials that produce flowers all summer long. The plants are erect and spreading, 2-3 ft (0.6-0.9 m) tall and just as wide. They have numerous branches and opposite, pointed leaves 2-4 in (5-10 cm) long. The fragrant flowers are borne singly or in clusters, and can be red, magenta, pink, yellow or white, sometimes with more than one color on the same plant. Bicolored flowers are also possible. Individual flowers are trumpet shaped, about an inch across at the end and about two inches long. They open in the evening and wilt the next morning, but the plants continue to produce new flowers from late spring 'till fall. Four o'clocks have large, black carrot shaped tubers that can be a foot or more long. In warm regions, the roots can weigh up to 40 lb (18 kg) or more.
Hybrids between this species and M. longiflora are available. The 'Jingles' cultivars are smaller with multi-colored flowers.
Four o'clocks are native to tropical South America. They have become naturalized in many parts of the Southern U.S.
Fast growing four o'clocks are easy to grow and essentially trouble free, thriving in most any soil. Light: Four o'clocks do best in full sun, but also perform well in partial shade. Moisture: Regular garden moisture. Reduce watering in winter. Hardiness: USDA Zones 7-11. Four o'clocks are perennial sub-shrubs in zones 10 and 11. They are grown as annuals in cool regions. To grow them as returning perennials, lift the tubers in fall and store in a frost-free location. In zones 7 through 9, four o'clocks can be mulched with straw for overwintering in the garden. Propagation: Plant seeds in early spring or divide tubers any time. If you soak the large black seeds in water overnight before planting they will germinate quicker. If you get one that you like especially, you can dig up the tuber at the end of the season and replant it next spring. Four o'clocks will self seed. The large, elongate tubers make it difficult to transplant very large specimens.
Even when they're not awake the four o'clocks are colorful characters like this one still sound asleep at 6:00 PM. Download a large version (800x600) of this image.
Four o'clocks are rugged little perennials, long popular in southern gardens, and often persisting even after the garden has been abandoned. Use four o'clocks in beds, in the perennial border, or (in frostfree climates) use them in mixed hedges. Here in North Florida, four o'clocks usually open up around 8 o'clock in the evening! But they open earlier on rainy or very cloudy afternoons. The stems are rather fragile and brittle and often get broken. A sweetly scented four o'clock growing near the front door is a pleasant southern tradition.
Within its natural range in South America, the root of the four o'clock is used medicinally and as a hallucinogen. The flowers are used for making dyes. The flowers actually have no petals - what looks like the corolla is in fact the calyx, but only a botanist would appreciate the distinction!
Four o'clocks self seed and may become a nuisance if not kept under control. If left to spread unchecked, they then can be difficult to eliminate because of the large, deep-rooted tubers. All parts of the plant are said to be poisonous - do not ingest!