Cool season zone
From PLANTFACTS.OSU.EDU
1. An area of North America, comprised of Canada and roughly the northern third of the continental United States, where climatic conditions support a specific group of turfgrass cultivars; cool season turfgrasses are adapted to maximum growth under temperatures of 60 to 75° F during the growing season.

The cool season zone is above the transition zone in this example.
Source: Ohio State University Turfgrass Program
