Bermuda grass is a warm-season turf species prized for its resilience and ability to thrive in hot climates, especially throughout the southern United States. While it maintains a vibrant green color during the summer, the expectation that it remains green throughout the entire year is generally incorrect. This turfgrass is biologically programmed to react to cooler temperatures, meaning that in most regions, Bermuda grass will inevitably transition out of its active, green state. Understanding the seasonal behavior of this grass involves looking closely at its survival mechanisms and the environmental factors that dictate its color.
The Onset of Winter Dormancy
The reason Bermuda grass does not stay green year-round is its natural process of winter dormancy, which is a survival strategy. This change is triggered when ambient temperatures drop consistently, signaling the plant to conserve energy. The biological switch occurs when soil temperatures, measured at a four-inch depth, fall below approximately 55 to 60 degrees Fahrenheit, causing the grass to stop producing new growth and chlorophyll.
The loss of chlorophyll, the green pigment responsible for photosynthesis, changes the grass’s appearance from green to a tan or straw-brown color. The above-ground leaf blades enter a state of inactivity, but the plant itself is not dead. Its roots, rhizomes, and stolons remain alive underneath the surface, storing carbohydrates to fuel the spring re-emergence. This dormant state protects the turf from cold weather and frost until warmer temperatures return.
Climatic Factors That Influence Color
The geographical location heavily influences the length and severity of the Bermuda grass dormancy period. In regions classified as the transition zone, which experience both hot summers and cold winters, the grass is guaranteed to turn brown and remain dormant for several months. This zone presents a challenge because the climate supports neither exclusively warm-season nor cool-season grasses year-round.
Conversely, specific areas with consistently warm, subtropical, or tropical climates may allow Bermuda grass to maintain its green color through the winter. Locations like Southern Florida or parts of the Southern California coast often have soil temperatures that rarely drop below the 55-degree Fahrenheit threshold. In these mild environments, the grass may merely slow its growth rather than entering a full dormancy, allowing it to retain an acceptable color year-round.
Maintaining Green Color in Cooler Weather
For lawn owners in areas where dormancy is unavoidable, the most popular method for keeping a green lawn in winter is winter overseeding. This technique involves planting a cool-season grass, most commonly perennial ryegrass, directly into the existing Bermuda grass turf in the early fall. Overseeding should be timed when nighttime temperatures begin to drop consistently into the 60 to 70-degree Fahrenheit range, typically about a month before the first expected frost.
The process begins by “scalping” or mowing the Bermuda grass very low, which reduces competition and allows the new seed to reach the soil. Perennial ryegrass seed is then spread over the lawn at a rate of 10 pounds per 1,000 square feet for a dense, uniform winter cover. The newly seeded area requires frequent, light watering, often twice daily, to keep the seeds moist until they germinate, which usually occurs within seven to ten days.
Turf Colorants
As an alternative, some homeowners and turf managers use specialized turf colorants or dyes. These products are non-toxic, green pigments formulated to be sprayed directly onto the dormant, brown leaf blades. Turf colorants provide an instant, natural-looking green appearance that can last for up to three months, depending on the grass growth rate and mowing frequency. This option is more cost-effective and requires less water and maintenance than overseeding. It also offers the benefit of slightly warming the turf surface, which can aid in the Bermuda grass’s spring green-up.