Across many regions, it is a common sight to see a green lawn turn brown once winter arrives. Whether your grass stays green in winter depends entirely on the type of turfgrass you have and the severity of your local climate. This seasonal color change is not a sign of a dying lawn, but rather a survival strategy that allows the grass to endure freezing temperatures and limited resources. Understanding this biological process helps explain why some lawns remain green while others appear to take a long nap until spring.
The Biological Mechanism of Dormancy
The change in color from green to brown is a visible sign that the grass has entered dormancy, a protective mechanism against environmental stress like cold or drought. During this period, the grass redirects its energy away from producing new leaf tissue, focusing instead on protecting its crown and root system. This shift ensures the plant’s core remains healthy beneath the soil, ready to resume growth when conditions improve. Chlorophyll, the green pigment responsible for photosynthesis, breaks down when temperatures drop below a certain threshold. As the existing chlorophyll breaks down, the grass blades lose their green hue, revealing the underlying straw-like color. The grass is not dead; it is simply in a suspended state of growth, conserving energy to survive.
Cool-Season Versus Warm-Season Grasses
The most significant factor determining winter color is the distinction between the two major categories of turfgrass: cool-season and warm-season varieties.
Cool-Season Grasses
Cool-season grasses, such as Kentucky Bluegrass, Tall Fescue, and Perennial Ryegrass, are best suited for northern climates and the upper two-thirds of the United States. These grasses thrive in temperatures between 60°F and 75°F and are much more tolerant of cold weather. Cool-season turf will slow its growth but typically remains green during the winter in milder climates or during periods of relatively warm weather. They have adapted to continue a limited amount of photosynthesis even in cooler conditions, maintaining their green color. However, even these grasses will enter a temporary state of dormancy and turn brown if faced with a prolonged, severe freeze or drought.
Warm-Season Grasses
Warm-season grasses, which include popular varieties like Bermuda, Zoysia, and St. Augustine, are common in the Southern United States. These grasses prefer high temperatures, with optimal growth occurring between 80°F and 95°F. Once soil temperatures consistently fall below 65°F, warm-season grasses go completely dormant, resulting in a uniform tan or brown color. This color change is a necessary survival mechanism for warm-season lawns during the winter months. For homeowners in the South who desire a green lawn year-round, the common practice is to “overseed” the dormant warm-season turf with a temporary cool-season grass like Perennial Ryegrass in the fall. This provides a temporary green cover until the warm-season grass naturally greens up again in the spring.
Caring for Dormant or Brown Grass
Caring for grass in its dormant state requires a shift in maintenance priorities to protect the plant’s health. The brown appearance can be deceiving, but the roots and crown are still alive and vulnerable to damage. It is important to minimize all foot traffic on dormant turf, especially when the ground is frozen. Traffic on frozen grass blades can cause them to break and fracture the living crown tissue, leading to dead patches in the spring.
Dormant grass requires less water than actively growing grass, but it is not immune to desiccation, or drying out. During a prolonged dry period in winter, a light watering may be beneficial to prevent the roots from completely dehydrating.
Ensure the lawn is clear of any thick layers of leaves or debris. This organic matter can smother the turf, block sunlight, and trap excessive moisture, which can lead to fungal diseases like snow mold. By protecting the dormant crown and roots throughout the coldest months, the grass is well-positioned to recover and turn green once soil temperatures rise again in the spring.