As grass transitions from summer growth to winter dormancy, lawn care practices require a significant shift. The way grass is mowed directly impacts its ability to survive the cold season and thrive in the spring. Fall mowing is a strategic process aimed at building up the plant’s internal reserves for successful overwintering. Properly adjusting the cutting height ensures the turf is resilient enough to endure winter stress and protected from common seasonal diseases.
Understanding the Purpose of Fall Mowing Height
During early and mid-fall, the primary goal for cool-season grasses is to produce and store energy in their root systems before growth ceases. This energy storage is accomplished through photosynthesis, requiring sufficient leaf surface area to capture sunlight effectively. The carbohydrates created are then moved to the crowns, rhizomes, and roots to serve as fuel for winter survival and the initial spring growth spurt.
Maintaining a moderate height, often slightly higher than the summer cut, maximizes this photosynthetic capacity. Cutting the grass too short too early limits energy production and carbohydrate accumulation, leaving the plant with insufficient reserves to withstand the cold. Conversely, if the grass is allowed to become too tall, the dense canopy can trap moisture and create an environment susceptible to fungal diseases like snow mold.
The Gradual Reduction in Mowing Height
The best practice for preparing the lawn for winter involves a controlled, gradual reduction in the mowing height over several weeks in the fall. This process allows the grass to adjust to the lower height without experiencing severe stress, which would otherwise force it to use stored energy for rapid leaf regrowth.
The core principle guiding this transition is the “one-third rule,” which dictates that no more than one-third of the grass blade’s total height should be removed in any single mowing session.
For instance, if the summer height was maintained at 3.5 inches, the first reduction might bring the height down to approximately 2.5 to 3 inches. Subsequent mowings should continue to follow the one-third rule, lowering the deck one notch at a time until the desired pre-winter height is reached. This staggered approach, often involving a reduction of about half an inch per cut, prevents the plant from being excessively defoliated, which can shock the root system and compromise its health. Following this progressive reduction maintains a healthy balance between leaf area for energy production and a manageable height for disease prevention.
The Critical Final Cut Before Winter
The definitive answer to whether grass should be cut shorter in the fall is found in the final mow of the season, which should be the lowest cut. This final cut, typically performed just before the grass enters full dormancy, is essential for minimizing potential winter damage. The recommended height for this final cut is generally between 2 and 2.5 inches for most cool-season grasses.
Cutting the grass to this lower height serves multiple protective functions. It significantly reduces the amount of plant material that can mat down under heavy snow cover, which encourages the development of snow mold fungus. A shorter turf height also makes the lawn less attractive as a habitat for small rodents, such as voles, which often nest and feed under a tall canopy during winter.
This last cut should occur after the final growth spurt of the season, usually following the first hard frost, when the grass blades stop actively growing. Performing the cut too low, however, can expose the crown of the grass plant to damaging cold, so the 2-inch minimum is important for protection.