Gravel culture was the most widely used hydroponic technique from the 1940s through the 1960s. During the late 1960s and early 1970s one commercial operation, Hydroculture, near Phoenix, Arizona, had almost 20 acres (8 ha) of greenhouses in gravel culture. Many smaller commercial greenhouses throughout the United States used gravel culture as it was well documented and several companies such as Hydroculture were selling “mom and pop” packages to people interested in setting up their own hydroponic greenhouse.