Autumn mowing is a strategic transition phase, preparing the turf for winter dormancy. This final stage of lawn care involves height reduction with the ultimate goal of strengthening the grass plant for spring growth. Adjusting the mower blade height correctly helps the turf store energy and reduces the likelihood of winter diseases and damage. The process centers on gradual, precise adjustments that maximize the lawn’s ability to survive cold and snow cover.
The Ideal Cutting Height for Autumn
Fall mowing involves a measured, incremental reduction in height over several weeks to ease stress on the grass plant. If cool-season lawns, such as Kentucky bluegrass or fescue, were maintained at three to four inches during summer, begin dropping the blade setting incrementally. The goal is a final height of approximately two to two and a half inches before the season ends.
This gradual approach follows the one-third rule, which advises against removing more than one-third of the grass blade length at any single mowing session. Achieve this by lowering the blade one notch or about one-third of an inch per mowing until the desired length is reached. If you mow weekly, this reduction will occur over three to four separate sessions, allowing the grass to adjust without shocking the root system.
Warm-season grasses, like Bermuda or Zoysia, heading into full dormancy, require a lower final cut, often between one and a half to two inches. However, varieties such as St. Augustine should be maintained slightly higher, around two and a half to three inches, to protect sensitive stolons. This shorter height for warm-season turf helps prevent the buildup of dead leaf material, known as thatch, which can be problematic during dormancy.
Determining the Final Cut
The final cut of the season is based on weather patterns, not a specific date. Continue mowing at the reduced height as long as the grass exhibits visible growth. For cool-season grasses, growth slows significantly when sustained air temperatures drop below 50 to 55 degrees Fahrenheit.
The growing season ends when the ground temperature drops low enough for a hard freeze. A hard freeze is defined as air temperatures falling to 25 to 28 degrees Fahrenheit for several hours. This sustained cold signals the cessation of physiological activity in the grass plant, eliminating the need for further mowing. The final cut, done at the lowest height, should occur just before the first expected permanent snow cover.
Why Proper Fall Height Matters for Turf Health
Maintaining the correct fall cutting height directly influences the grass plant’s ability to survive winter and thrive the following spring. In autumn’s cooler temperatures, grass blades continue photosynthesis, converting sunlight into carbohydrates (primarily fructans) that are translocated to the roots and crowns. These stored sugars serve as the plant’s food reserves during winter dormancy and fuel the initial spring growth spurt.
Cutting the grass too short too early removes too much photosynthetic area, limiting this energy storage process. Conversely, leaving the grass too long (above three inches) creates a significant risk for fungal diseases, specifically snow mold.
When tall grass is pressed down by snow, it mats easily, trapping moisture and creating an ideal environment for Microdochium and Typhula fungi to flourish. The shorter, two to two-and-a-half-inch height allows the turf to stand up better under snow load, improving air circulation and sunlight exposure at the crown level. This reduced height also offers less protective cover for small rodents, such as voles, which can cause feeding damage under the snow layer.
Post-Mowing Preparations for Winter
After the final cut, several non-mowing tasks ensure the lawn is fully prepared for winter.
Leaf and Debris Removal
The most immediate concern is the complete removal of all fallen tree leaves and debris. A thick layer of matted leaves will smother the grass, blocking sunlight and promoting moist conditions that favor snow mold development. Leaves should be raked, mulched into fine particles, or bagged to expose the turf to air and light.
Deep Watering
A final deep watering is beneficial, particularly if the fall season has been dry, as it prevents winter desiccation. Water-saturated soil retains heat more efficiently than dry soil, helping to insulate and protect the grass roots from extreme cold. This watering should be done just before the ground freezes solid to ensure maximum hydration reserves.
Winterizing Fertilizer
Applying a winterizing fertilizer provides necessary nutrients for root health over the dormant period. This late-season feeding should feature a low-nitrogen, high-potassium (K) formula, such as an NPK ratio around 12-0-24 or 8-12-16. Potassium strengthens the grass plant’s cell walls, enhancing cold tolerance and overall hardiness against winter stresses.