Grass grows significantly slower in the fall as part of a natural process to prepare for winter dormancy. This slowdown is a biological shift triggered by changes in the environment, not a sign of poor health. The grass plant actively transitions its focus from rapid blade growth to building internal reserves to survive the cold months ahead. Understanding this seasonal change is important for adjusting lawn care practices to promote long-term turf health.
The Science Behind the Slowdown
The decrease in above-ground grass growth is primarily a reaction to two environmental signals: temperature and light. Cooler air and soil temperatures directly affect the speed of the plant’s metabolic processes. Since biological reactions are temperature-dependent, reduced warmth slows the rate of cell division necessary for new leaf growth.
Cool-season grasses, like Kentucky bluegrass and fescue, thrive between 50 and 65 degrees Fahrenheit, but growth decelerates significantly once the temperature consistently drops below 50 degrees Fahrenheit. Warm-season grasses, such as Bermuda grass, react more dramatically, often entering full dormancy when temperatures fall below 50 to 55 degrees Fahrenheit. Furthermore, the decreasing length of the day, known as photoperiodism, limits the amount of time the grass can perform photosynthesis. Less available sunlight and less intense rays mean the plant has less energy to allocate toward producing new blades.
Shifting Focus: Prioritizing Root Health
Even though blade growth slows noticeably, the grass plant remains highly active underground in a process known as “hardening off.” This internal shift redirects the energy produced during the day into the root system and crowns for storage. The plant stockpiles carbohydrates, which are complex sugars that act as an energy reserve.
This buildup of carbohydrate reserves is essential for the plant’s survival through winter stress and disease. The stored energy acts as the fuel source for the plant to repair damage and resist frost throughout the dormant period. When spring arrives, these reserves provide the immediate energy needed to kickstart root growth and the initial flush of green blades. The strength of spring growth is directly related to the amount of energy the grass successfully stored in its roots and lower stems in the fall.
Adjusting Your Autumn Lawn Care Routine
The grass’s shift in focus means that maintenance routines must change to support winter preparation.
Mowing
Mowing should continue as long as the grass is growing, typically until the first hard frost. The final few cuts of the season should gradually lower the height to about two to two and a half inches. This shorter height helps prevent the blades from matting down under snow cover, which reduces the risk of fungal issues like snow mold.
Fertilization
Fall fertilization is considered the most important application of the year for many turf types. A specialized fall fertilizer, often high in nitrogen and potassium, should be applied when grass growth is slowing but roots are still active. Nitrogen supports the deep green color and steady growth, while potassium strengthens the roots and helps the plant efficiently transport and store carbohydrates. Applying this nutrient boost helps the grass build its vital winter pantry.
Watering and Cleanup
Watering needs change, as cooler temperatures and increased rainfall reduce the rate of evaporation. While the frequency of watering should be reduced, the grass still requires sufficient moisture to support active root growth and nutrient uptake. Ensure the soil remains adequately moist until the ground freezes, as roots need water to move nutrients into storage areas. Prompt removal of fallen leaves is also necessary, as a thick layer blocks limited sunlight and traps moisture, leading to disease.