Family: Poaceae

Origin, Description & Uses
Poa pratensis, commonly known as Kentucky bluegrass, is a cool-season perennial grass native to much of the subarctic and temperate Northern Hemisphere, as well as northern Mexico. It is widely recognized for its fine-textured blue-green leaves and dense, spreading growth habit created by underground rhizomes. Kentucky bluegrass is commonly used for lawns, pasture, erosion control, recreational fields, and turf because it forms a durable, attractive ground cover that tolerates grazing and mowing. In Hawai‘i, this species has become naturalized in disturbed mesic to subalpine forests and alpine environments at elevations of approximately 1,220–4,025 m on O‘ahu, Maui, and Hawai‘i Island.

Risks & Threats
Kentucky bluegrass is naturalized in Hawai‘i and possesses traits that are cause for concern in tropical island ecosystems. Its vigorous rhizomatous growth allows it to spread and form dense mats that can outcompete native alpine and subalpine vegetation, especially in disturbed habitats. The species can alter plant community composition, reduce native biodiversity, and potentially change soil and ecosystem processes in sensitive high-elevation environments. Because it is already established in parts of Hawai‘i, further planting and intentional spread should be avoided, particularly near natural areas and native ecosystems where it is not yet widespread. When possible, choose low-risk or native grass alternatives for landscaping, restoration, and erosion control projects. In areas where Kentucky bluegrass is already common, careful management and prevention of further spread can help minimize additional ecological impacts.

High Risk Traits:

• Environmental weed – outcompetes natives
  
• Congeneric weeds (e.g., P. annua)
  
• Broad climate adaptability
  
• Naturalized on multiple continents (incl. Hawaii)
  
• Planted intentionally by people
  
• Spreads via rhizomes & tillers
  
• Self-compatible / apomictic (no outcrossing needed)
  
• Hybridizes naturally
  
• Persistent seed bank (years to decades)
  
• Prolific seed production (>1000/m²)
  
• Dispersed as crop seed contaminant
  
• Seeds survive animal gut passage
  
• Tolerates mowing/grazing

Low Risk Traits:

• No spines, burrs, or thorns
  
• Palatable (no grazing deterrent)
  
• Non-toxic to animals or humans
  
• No wind/water/bird/animal external dispersal
  
• Well controlled by herbicides