Wild Four O'Clock
Mirabilis nyctaginea
Washington State Classification
Class A — Eradication Required Statewide
It is a weedy plant that is capable of establishing in a wide range of habitats.
Quick Reference
Identification
Growth Habit
It is a perennial herb, sometimes woody at the base, reaching 3 to 4 feet tall. It has a thick, black taproot that can extend downward for two feet. The name refers to the flowers, which open late in the day and whither early the next morning.
Leaves
Leaves are oppositely arranged, heart-shaped to egg-shaped and 2-4 inches long and 1-3 inches wide. The lower to middle leaves are attached by a petiole (leaf stem). Upper leaves may be sessile (no leaf stem). Leaves are waxy and usually hairless.
Flowers
Flowers are about 3/8 in diameter and are in clusters of 3 to 5 growing from a short, hairy flowerstalk at the tips of the plant. A whorl of bracts is found at the base of each flower. The flowers have 5 reddish to lavender sepals and no petals.
Fruit & Seeds
Seeds are prominently five-ribbed, warty, somewhat hairy, grayish brown in color and ranges from 1/8 to 1/4 inch in length.
Impact
It is a weedy plant that is capable of establishing in a wide range of habitats. In Washington it has shown the ability to spread from a small 10 acre site to several hundred acres. It is capable of impacting agricultural and range lands.
Ecology & Spread
Habitat
Wild four o'clock is found in a range of habitats in eastern Washington, including orchards, alfalfa fields, rangeland, right-of-ways and disturbed areas. It can also grow along riverbeds, and in sandy, rocky, and heavily cultivated soils. Please click here to see a county level distribution map of wild four o'clock in Washington.
Spread Mechanisms
Reproduction
It reproduces by seed and by fragmented root pieces. Seed is set from July to September. The involucre aids in the dispersal of the seeds, acting as a small umbrella which catches on vehicles.
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Control Methods
Mechanical
- Hand pulling is not recommended because the stems break at the crown. The roots are strongly branched, and broken root pieces will produce sprouting. Small infestations can be spaded or dug up. Repeated mowing or cultivation will prevent seed production and lower the seed bank. Eventually the plant will die from loss of nutrient reserves stored in the root. Plow infested meadows and plant a cultivated crop for 2 years. Hoe out remaining plants.