MTC TURF NEWS: Jay McCurdy Ph.D., Associate Professor, Turfgrass Extension Specialist Department of Plant & Soil Sciences, Mississippi State University

This is the first article of a multi-part series detailing the origins and future of turfgrass.

Turf consists of a layer of various plants cultivated to form a uniform ground cover, typically one that can tolerate foot traffic and routine mowing. The first known use of the word turf occurs before the 12th century and refers to the “upper stratum of soil bound by grass” (Merriam-Webster, 2022). Objectively, turf only exists in human-maintained systems; however, the species comprising various turf scenarios long predate human interference.

Those turfgrass species most frequently selected for turf scenarios have been subject to environmental pressures (notably, frequent grazing) that have selected for traits that enhance their value as turfgrasses. Valuable traits include color, texture, uniformity, growth habit, and durability under stress. Plant breeding, the introduction of non-native and exotic species, and recurrent selection for desirable traits have led to modern cultivars and varieties of turfgrass that predominate in maintained turf settings such as lawns, sports fields, golf courses, sod farms, and roadside rights-of-way.

Turfgrasses are typically narrow-leaved species of relatively short stature that are somewhat regularly mown at heights of approximately four inches or less (Thompson and Kao-Kniffin, 2017). By convention, all grasses, including turfgrasses, belong to the Poaceae family of monocotyledonous flowering plants. The monocotyledonous (monocot) clade includes grasses and grass-like flowering plants with seeds that contain only one embryonic leaf (also known as a “cotyledon”). Monocots offer few obvious advantages for turf applications, as other flowering plants in the dicotyledonous clade (having two embryonic leaves) also persist under typical mowing heights as weeds or amenity forbs within various turf scenarios.

Not Just Grass

Turfgrasses are broadly classified as cool- or warm-season plants. Cool-season species are the predominant turfgrass species in climates with cold winters and mild summers, as well as adequate soil moisture. Warm-season species predominate in climates with mild winters and hot summers. The overlapping area between the two is termed the transition zone, where cool- and warm-season species grow equally successfully.

Cool-season species have evolved a C3 photosynthetic pathway for carbon fixation. They use an enzyme (called RuBisCO) to fix CO2. That carbon from CO2 forms a three-carbon sugar and then goes on to fuel plant growth and metabolism. Alternatively, warm-season species have evolved a C4 photosynthetic pathway that produces a four-carbon sugar. Plants with the C4 pathway have improved metabolism and a competitive advantage over C3 plants under conditions of drought, high temperatures, and limited nitrogen or CO2.

Cool- and warm-season species have different optimal temperatures for growth and metabolism. Warm-season species grow best when temperatures are above approximately 80°F and enter dormancy below their “base growth temperature” of around 50°F. Alternatively, cool-season species grow best when temperatures range from 60–75°F. Cool-season species enter a state of winter dormancy at temperatures below freezing and are often considered dormant during summer conditions that exceed their ideal growing temperatures, especially when soil moisture is limited. Growth models to predict the suitability and phenology of these species are largely based upon these parameters and estimates.

There are approximately 40 million acres of turfgrass in the United States (2% of the total U.S. land cover) (Milesi et al. 2005). Several estimates suggest that residential lawns represent roughly 75% of U.S.