The cessation of grass growth each year is a natural biological event signaling the transition from the growing season to winter survival. This stopping of upward blade growth is preparation for dormancy, a state similar to hibernation in animals or leaf drop in deciduous trees. The timing of this slowdown is not fixed to a calendar date, but is governed by environmental signals that tell the grass plant it is time to conserve energy. Understanding these factors is the basis for proper late-season lawn care and ensuring a healthy return to green in the spring.
Environmental Triggers for Growth Stoppage
The primary factor dictating when grass growth slows is temperature, specifically the temperature of the soil and the air. Most turfgrass varieties significantly slow or cease vertical growth when the ambient air temperature consistently falls into the 50 to 55-degree Fahrenheit range.
The second signal is the shortening photoperiod, which is the decreased duration of daylight hours. As autumn progresses, the decreasing amount of sunlight triggers biochemical changes within the grass plant. These two factors—falling temperatures and reduced light—work together to initiate the plant’s defense mechanism against winter conditions.
Understanding Grass Dormancy
When growth stops, the grass enters dormancy, a survival strategy that protects the plant from cold and low-light conditions. Dormancy is characterized by a significant slowdown of the plant’s metabolic processes. The grass may turn a dull tan or brown color, which is a visible sign that the plant is conserving moisture and energy.
The grass plant redirects its energy and carbohydrate reserves away from producing new leaf blades and focuses on storing them in the underground crown and root system. These stored carbohydrates sustain the plant through the cold months and provide the fuel needed for the rapid green-up in spring. While vertical growth stops, the root system of cool-season grasses may continue limited activity until soil temperatures drop to near freezing, often around 33°F.
Timing Differences by Grass Type and Climate
The exact timing of growth cessation depends heavily on the specific type of grass and the regional climate.
Cool-Season Grasses
Cool-season grasses, such as Kentucky Bluegrass and Fescue, are cold-tolerant. These grasses often maintain some level of green color and slow growth until late fall, generally in late October or November, when sustained cold weather arrives.
Warm-Season Grasses
Warm-season grasses, including Bermuda and Zoysia, thrive in heat and are much more sensitive to the cold. Their growth stops much earlier, typically when soil temperatures consistently fall below 50 to 55°F. This can happen in early to mid-fall, often in September or October in the transition zone. These grasses quickly enter a brown, dormant state as soon as the nights become consistently cool.
Preparing the Lawn for Winter Stop
The final weeks before the lawn enters dormancy require specific maintenance actions for spring health. One important step is the final cut of the season, which should leave the grass blades shorter than the summer height. For most cool-season grasses, the target height for the last mow is between 2 and 2.5 inches. Cutting the grass lower helps prevent the blades from matting down under heavy snow cover, reducing the risk of fungal diseases like snow mold.
This is also the ideal time for a late-fall fertilizer application, often referred to as “winterizing” fertilizer. This application maximizes the storage of carbohydrates in the roots, bolstering the plant’s reserves for winter survival and promoting a quicker green-up in the spring. Finally, all leaves and debris must be cleared from the lawn to prevent smothering the grass and creating an environment where diseases can thrive.