Pop Quiz: How does the Colorado Water Plan define non-functional turf?
A. Grass no one uses.
B. High-water-using turf where alternative landscaping types may reduce water use
C. Turf not needed to serve a human function, not in a yard, not on a sport field.
D. Turf whose only purpose is to lower air temperature
Answer: B
Bluegrass turf, and other cool-season groundcovers, have become a hot topic of conversation in the arid and semi-arid southwest. Traditionally cultivated in yards, parks, schools, and other areas across the United States, bluegrass turf has increasingly been excluded or reduced in southwest landscaping, and for good reason. In parts of Colorado, the irrigation requirement for bluegrass may be over twice the requirement for well-watered trees and a tough comparison with native plants that require no irrigation after establishment.
With increasing concerns about the future of the Colorado River, the yield of other native water supplies, increasing demands due to population growth and development, and concerns that lawns are becoming more thirsty due to climate change, communities across the southwest have questioned whether bluegrass turf, particularly “non-functional turf” is a necessary part of their landscapes. The Colorado Water Plan defined non-functional turf as “high-water-using turf on slopes, in medians, or other locations where alternatives like low-water vegetation, mulch or hard-scapes may reduce water use”. Colorado efforts to reduce non-functional turf include House Bill 22-1151 and the Colorado Water Conservation Board’s (CWCB) related turf replacement program, which can provide funds for eligible entities to start or further support their own turf replacement programs.
Potential benefits of turf replacement include reduced irrigation requirements, lower use of fertilizers and harmful pesticides/herbicides, lower labor cost for mowing and maintenance, and increased biodiversity in the landscape. Potential downsides include the cost of replacing turf with higher-maintenance landscapes, although Colorado Springs has shown that replacing turf with low-maintenance native grasses can be a lower-cost solution long term with a one to five year return on investment.
Another potential downside of turf replacement may be an increase in the urban heat island effect. A study from the Desert Research Institute compared surface and air temperatures in bluegrass landscapes (high irrigation), oasis landscapes (moderate, targeted irrigation), and xeric landscapes (no irrigation). At the study site in Arizona, daytime and nighttime air temperatures were compared between these three landscape types. While the coolest nighttime air temperatures were measured in the bluegrass landscape (with the xeric and oasis landscapes having warmer temperatures), the coolest daytime air temperatures were actually measured in the oasis landscape, which used significantly less irrigation than the bluegrass landscape. The results from this study suggest that the urban heat island effect can be mitigated by replacing removed turf judiciously with lower water use plants (or even shade structures) that provide shade and cooling while using less water than turf.
