Preparing a lawn for winter dormancy requires managing grass height in the fall, which directly impacts the turf’s health the following spring. Adjusting the mowing strategy is a calculated measure to protect the grass crown, promote root health, and prevent disease over the cold months. Understanding the correct height and timing for the final cuts optimizes the grass plant’s ability to survive winter without fungal issues or cold damage.
The Strategy for Adjusting Mowing Height
Homeowners should adopt a gradual reduction strategy for the mower deck in early fall to prepare the lawn for winter. This involves slowly lowering the cutting height over several mowing sessions, avoiding a single, drastic cut. Suddenly removing too much blade stresses the grass plant and interrupts its ability to photosynthesize effectively before dormancy.
For cool-season grasses (like Kentucky bluegrass and fescue), the final cut should be between 2.5 and 3 inches. While 3 to 4 inches is recommended during the growing season to shade the soil and support deeper roots, fall growth slows naturally. Decrease the height by about one-quarter to one-third of an inch with each subsequent mow until the final height is reached.
This gradual approach prevents shocking the grass plant, which could lead to browning or weakened turf. Avoid scalping the lawn (cutting significantly below 2 inches) as it removes too much leaf tissue. An aggressive cut damages the crown, the growing point of the plant, leaving it vulnerable to winter injury.
Biological Reasons for the Final Height
Maintaining the correct final height is necessary for the grass plant’s winter survival. A blade length of 2.5 to 3 inches allows for continued, reduced photosynthesis into the late fall. This process produces and stores carbohydrates in the crown and roots, providing the energy reserves needed to survive dormancy and initiate spring growth.
The grass crown, located near the soil line, is protected by a sufficient layer of leaf tissue. This layer insulates the delicate growing point from extreme temperature fluctuations and harsh winter elements, such as freeze-thaw cycles. Cutting the grass too short removes this protective layer, leaving the crown exposed and susceptible to cold injury.
Leaving the grass excessively tall (above 3 inches) presents risks primarily related to disease. Long blades mat down under snow and ice, creating a dense, moist environment at the soil surface. This condition is ideal for fungal diseases, such as snow mold, which damages turf when the snow melts. A shorter, non-scalped final cut minimizes matting risk and promotes better air circulation.
Timing the Transition and Final Cut
The transition to a lower mowing height should begin when the grass’s growth rate naturally slows due to cooling temperatures. For cool-season grasses, this typically occurs when daytime high temperatures consistently drop into the 50 to 55°F range. The shift in weather, rather than a specific calendar date, should dictate the start of the height reduction process.
The last cut of the season should be timed just before the grass enters complete dormancy. This usually coincides with the first hard frost or when the air temperature consistently remains below 40°F for an extended period. Once temperatures are consistently this low, the grass stops growing, signaling the season’s final trim should be completed.
Avoid mowing when grass blades are frozen or covered in frost, as this can shatter the frozen cells and cause significant damage. Timing the final cut about a week before the predicted hard frost ensures the grass is at the optimal 2.5 to 3-inch height for winter protection. This final mowing reduces exposed leaf tissue while leaving enough blade length for energy storage and crown insulation.