Bermudagrass (Cynodon dactylon), a warm-season grass, is widely used for lawns, turf and golf courses. Warm-season grasses like temperatures between 85 and 90 degrees Fahrenheit; they are typically green in summer and go dormant, turning brown in winter, returning to green in warm spring weather. Bermudagrass spreads by invasive underground stems called rhizomes and above-ground runners called stolons.
Climate Limits Northern Exposure
Grasses are grouped according to broad climate areas. The United States National Arboretum lists four basic grass-growing zones: cool humid, cool arid, warm humid and warm arid. Bermudagrass is found in both the warm humid and warm arid areas, roughly corresponding to U.S. Department of Agriculture plant hardiness zones 8 through 10. It grows best with average daily temperatures above 75 Fahrenheit and daytime temperatures between 95 and 100 F. The northern limit of growing Bermudagrass is those areas where the winter low temperatures rarely drop below 10 degrees F.
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Dormancy in Cooler Climates
As fall temperatures drop, Bermudagrass discolors and reserves of carbohydrates build in its rhizomes and stolons. When the average temperatures drop below 50 F, the stems and leaves stop growing and go dormant, but the rhizomes and stolons continue to grow for several weeks. Bermudagrass remains dormant until spring when average day and nighttime temperatures rise above 50 F for several days.
Dormancy in Frost-free Climates
If daytime temperatures are near 70 F, Bermudagrass will remain green through night temperatures as low as 34 F, although it grows slowly when cool nights begin in autumn and during the winter when shorter days reduce available sunlight. Bermudagrass roots, rhizomes and stolons will return to vigorous growth when soil temperatures are above 65 F, but the roots need soil temperatures roughly 80 F for best growth.
Drought and Dormancy
Bermudagrass evolved in subtropical and tropical climates with 25 to 100 inches of rainfall annually. In very dry conditions, Bermuda goes into a semi-dormant state. Rhizomes can lose 50 percent or more of their weight yet recover when they get water. If annual rainfall drops below 20 inches a year, you have to irrigate Bermudagrass to keep it green. You may have to water it occasionally in warm, windy weather to keep it from drying out.
Invasiveness and Spread
When Bermudagrass emerges from dormancy, you get your green back but you still have to deal with spreading stolons and rhizomes that grow from 1 to 6 inches below the soil. You have to till that deep to remove the rhizomes, but do not do this when the soil is moist because rhizome pieces will continue to grow. You can prevent the spread of rhizomes and stolons by withholding water during dry summer conditions, or by covering them with black plastic to deny them sunlight or with clear plastic in hot summer conditions to kill them by heat.