Too hot for the grass?
What happens to grass during a heatwave, and when can the plant no longer withstand the heat? These are questions that arise as the world rushes from one record to the next in terms of temperatures. Heatwaves are often paired with periods of low rainfall. According to climate scientists, both weather extremes will occur more frequently in the future. What will happen to the grass on the golf courses in Germany, Italy, Arizona or Dubai?
We asked Bernd Leinauer, who teaches as a professor at New Mexico State University and is involved in numerous turf research projects, including on golf courses in the southwest of the USA. At the same time, he is also involved in turf research in Europe.
“Generally speaking, cold zone grasses get too hot at over 100F or 37C. They can no longer cope with the temperature,” he notes. Cold zone grasses include all those varieties that can be found on golf courses in Northern Europe or North America, but some are also found in Italy or Spain. The common species that golfers are familiar with are Poa pratensis, Festuca or Agrostis varieties. “However, there is no strictly scientific study that has determined heat stress independently of the water supply,” Leinauer notes. To date, the survivability of grasses under heat has always been investigated in combination with the water supply.
Drought stress in the heat
Ultimately, that’s what golf courses are all about. The greater the heat, the more water the grass needs to cool down. In this context, scientists like Leinauer speak of evapotranspiration (ET), simply explained as the evaporation of moisture from both the soil and the plant. “Even if a golf course or sports field has an unlimited supply of water, the storage capacity of the soil and the irrigation window is limited. The water in the soil is used up by midday or early afternoon and the heat then leads to drought stress,” Leinauer explains the problem. “It has to be watered again, which is not always possible. Or grasses are used that require less water.”
Arizona, a state with around 400 golf courses, for example, experienced a heatwave in 2024 with more than 100 days with temperatures of over 37.7 degrees Celsius. However, warm zone grasses such as Bermuda or Zoysia can still cope well with what is difficult for the population to bear. For them, it only becomes uncomfortable between 43 and 46 degrees. This is also proven by a look at Dubai, where 49.9 degrees were measured on one day in 2024 and temperatures of around 45 degrees are not uncommon. Nevertheless, the golf courses there are in good shape. Their irrigation water is obtained from desalination plants. In these hot regions, “the issue of water consumption is central and is being addressed,” explains Leinauer. “Golf courses will have to close if the water runs out,” which could be the case in the USA in particular, where irrigation is largely carried out using groundwater or even drinking water.
This is why research has been carried out for decades into improving heat tolerance and reducing the water consumption of grasses through breeding. For Leinauer, however, it is clear that this is only one side of the coin: the other concerns “irrigation technology and irrigation quantity determination. There are considerable research shortcomings and implementation deficits in this area. There are big differences between what the grasses need and what is ultimately irrigated.”
