Bermuda grass is a popular, aggressive warm-season turfgrass known for its dense growth and high tolerance for heat and drought. Unlike cool-season varieties, this species is genetically programmed to enter a predictable period of rest, known as dormancy. This survival strategy is directly tied to declining environmental conditions, signaling the plant to conserve energy and survive the colder months.
Environmental Factors That Halt Growth
The cessation of active growth in Bermuda grass is primarily governed by a drop in temperature, especially within the soil profile. The plant’s metabolic rate begins to slow when air temperatures consistently fall below 60°F (15.5°C), reducing the need for mowing. The true trigger for the onset of dormancy, however, is the soil temperature, which provides a stable measure of the plant’s root environment.
Active shoot and root growth requires soil temperatures to be above 65°F (18.3°C). When soil temperatures, measured at a four-inch depth, drop below 55°F (12.8°C), the grass loses its ability to produce chlorophyll faster than it is degraded, causing the green color to fade. This threshold marks the point where the plant’s photosynthetic machinery shuts down, effectively halting growth.
Shorter day lengths, known as photoperiodism, also influence the plant’s hormonal signals for winter preparation. Cooler overnight temperatures accelerate the process, preceding the drop in soil temperature that fully initiates the dormant phase. This combination of dropping temperatures and reduced sunlight forces the plant to transition to a state of conservation.
The State of Dormancy
Once the environmental triggers are met, Bermuda grass enters dormancy, a protective survival mechanism that allows it to withstand freezing temperatures. During this state, the grass transitions from a vibrant green to a tan or straw-like color. The plant is not dead; it has simply ceased top growth and moved its energy reserves into its underground structures.
The root system, including the rhizomes and stolons, remains viable beneath the surface, protected from the cold. These underground structures hold the stored carbohydrates necessary for the plant to regenerate when conditions improve. This ability to survive winter as a root system defines its classification as a warm-season grass.
The grass remains in this dormant, brown state throughout the late fall, winter, and early spring, until sustained warmth returns. This period can last for several months, depending on the geographical location and the severity of the winter season. Dormancy insulates the plant against environmental stress, ensuring its return in the growing season.
Timing of Spring Regrowth
The grass will not resume active growth until it receives a reliable signal that the cold weather has passed. This signal is dictated by soil temperature, which must consistently rise above the dormancy threshold. For Bermuda grass to break dormancy and begin to “green up,” the soil temperature at a four-inch depth needs to reach and be sustained at 65°F (18.3°C).
A parallel condition required for spring green-up is that nighttime air temperatures must remain consistently above 60°F (15.5°C) for several consecutive days. These combined temperature requirements ensure the plant has enough warmth day and night to support the energy-intensive process of new growth. When these conditions are met, the grass begins to draw on its stored energy reserves to push out new leaf blades.
The timing of spring regrowth is variable and depends on the region’s microclimate and the specific weather patterns of the year. In warmer transition zones, green-up may occur earlier in the spring, while in cooler areas, it may be delayed until late spring. Monitoring soil temperature rather than air temperature is the most reliable way to predict the return of active growth.