Heat can turn Wimbledon's famous grass courts into an even faster, tougher surface. Here's the sports science behind how heat changes a grass court, and why it's a whole new game for players raised on clay and hard courts. Wimbledon is the only major played on a live surface. The Australian Open and U.S. Open are contested on hard courts, and the French Open is played on red clay. Neil Stubley, the All England Club’s head of courts and horticulture, and his team of 31 groundskeepers make sure that Wimbledon is always a picture-perfect spectacle thanks to constant maintenance. The 18 tournament courts and 20 practice courts for Wimbledon have been sown with perennial ryegrass since 2001.