Wild four o’clock

Identification & Biology
Alias' : heart leaf four o'clock, heart leaf umbrella-wort
Latin Name : Mirabilis nyctaginea
Category : Terrestrial Plants
Description :
  • Perennial herb with a large taproot up to 8 cm in diameter 
  • Mature plants can grow up to 1 m tall 
  • Branched square-like stems with nodes, woody at the base 
  • Leaves are opposite, simple, heart-shaped, 2.5-8 cm long, and usually have a pointed tip 
  • Flowers consist of five showy pink sepals with a whorl of bracts at the base 
  • Seeds are oblong, grayish-brown to yellow and appear warty or wrinkled 


Wild four oclock starts blooming mid-spring and can continue blooming into the hot summer months. It opens its flowers in the afternoon and closes them in the morning to target specific pollinators. Towards the end of the growing season, plants produce smaller flowers that are closed off from pollinators so that they may self-pollinate. The majority of the seeds fall close to the plant where they will germinate the following year, but self-propagation through root segments is also possible. The flowers of wild four o’clock are very similar to the related hairy four o’clock (Mirabilis albida), which is usually densely hairy all over. 


Wild four oclock prefers full sunlight and dry conditions, however partial sun is also tolerated. This plant grows in poor soil with a high content of clay, sand, or gravelly material. Wild four oclock has a strong preference for disturbed areas; it invades disturbed soils, orchards, rangelands, irrigation canals and ditches, riverbeds, waste areas and roadsides. Wild four o’clock is native to North America and its original area of distribution was from Texas to Saskatchewan, but it has since spread to each coast and is considered invasive.  

Impact & Risks
  • Wild four o’clock can spread rapidly and form acres of monoculture. 
  • It colonizes both perennial agriculture and rangelands, outcompeting native and pasture plants. 
Prevention & Mitigation

The most effective way to ensure that your lands do not become infested with wild four o’clock is by prevention. Here are some recommendations to prevent wild four o’clock from invading your property:  

  • Maintain your crops and natural lands in a healthy, vigorous condition to ensure a competitive plant community; competitive perennial grasses and forbs utilize water and nutrients that would otherwise be readily available to wild four o’clock.  
  • Clean footwear, vehicles and equipment prior to leaving areas infested with wild four o’clock.  
  • Regularly patrol your property for wild four o’clock plants and immediately control or remove infestations before seed set. Do not leave plants to compost as they may still produce viable seed.  
  • Cooperate with adjacent landowners and encourage them to prevent wild four o’clock spread.  
  • Immediately re-vegetate disturbed, bare soils with a suitable seed mixture that provides dense, early colonization to prevent weed invasion.  
  • Ensure soil, gravel and other fill material are not contaminated with seed.  
Treatment & Disposal
  • Most wild four o’clock infestations can effectively be controlled through mechanical treatments with the option of combining it with herbicide application.  
  • Handpulling 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 dug out. 
  • Repeated mowing or cultivation will prevent seed production and lower the seed bank.  
  • If agricultural fields or meadows are infested, plow and plant a cultivated crop for two years. Hoe out remaining plants.  
  • Before applying herbicides, read the label for full use and precautionary instructions.  For further information on the selection and application of chemicals to protect your crop, contact AgriService BC at 1-888-221-7141 or email AgriServiceBC@gov.bc.ca 
  • There are currently no biological control agents for use in BC.  
Okanagan Distribution

Priority Level Definitions

Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.