Whether lawn mowing is appropriate in cold weather depends on the grass’s physiological state and immediate temperature conditions. “Cold weather” usually refers to the late fall and early winter transition, when low temperatures signal the end of the active growing season but precede permanent snow cover. A strategic final cut is necessary for winter preparation. However, any mowing or traffic on grass that is frozen can lead to immediate and long-lasting damage.
Understanding Grass Dormancy
As temperatures consistently drop, turfgrass enters dormancy, a survival mechanism that conserves energy until warmer weather returns. Warm-season grasses, like Bermuda and Zoysia, are sensitive to cold and typically halt growth and turn brown when air temperatures fall below 65 degrees Fahrenheit or soil temperatures drop below 55 degrees Fahrenheit. This signals that the plant is focusing resources entirely on its root system for insulation and survival.
Cool-season grasses, such as Kentucky Bluegrass and Fescues, are more cold-tolerant and continue slow growth until temperatures remain consistently below 40 to 50 degrees Fahrenheit. This occurs as the plant shifts photosynthates—sugars produced during photosynthesis—down to the crown and roots. This reallocation ensures the plant has sufficient stored carbohydrates to survive the winter and green up quickly the following spring.
The Danger of Mowing Frozen or Frosty Grass
Regardless of whether the grass is cool- or warm-season, it should never be mowed or subjected to foot traffic when frozen or covered in frost. When the temperature drops below freezing, the water inside the grass blades freezes and expands, forming ice crystals. This ice makes the normally flexible cellular structure of the grass extremely brittle.
Applying any mechanical pressure, whether from a mower wheel, blade, or shoe, causes the fragile, ice-filled plant cells to rupture. The damage results in bruised, broken blades that turn a noticeable brown or black color within a day. This discoloration represents tissue death that will not heal until the grass resumes active growth in the spring, leaving the lawn vulnerable to disease and pests throughout the winter.
Preparing the Lawn for Winter (The Final Cut)
The last mow of the season is a strategic task, scheduled after the bulk of leaf drop but before the first hard ground freeze. The goal is to set the turf at an optimal height for winter survival, which involves a gradual reduction from the normal summer cutting height. For the final cut, the mower deck should be lowered to achieve a grass height of approximately 2 to 2.5 inches.
This specific height prevents several common winter lawn problems. If the grass is left too long, it can become matted down under heavy snowpack, creating an anaerobic environment conducive to snow mold, a damaging fungal disease. Furthermore, overly long grass provides shelter and nesting material for rodents, such as voles, which can damage the turf by tunneling and feeding on the crowns beneath the snow.
Cutting the grass too short, however, is equally detrimental because it removes the protective insulation that shields the crown, the most vulnerable growing point, from harsh winter desiccation and cold temperatures. The 2-to-2.5-inch target balances the need to deter mold and pests with maintaining enough blade surface for late-season photosynthesis and crown protection. This final cut should occur when the grass has slowed its growth rate significantly, ensuring the height remains consistent throughout the dormant period.
Mowing During Cold Snaps or Mild Winters
In regions prone to fluctuating weather, a cold snap is often followed by mild, sunny days that can stimulate renewed growth in cool-season grasses. If the temperature rises above 40 degrees Fahrenheit and the grass is visibly growing, intermittent mowing may be necessary to maintain the recommended winter height. If the grass is actively growing, it should be cut, provided the conditions are dry and the grass is completely unfrozen.
These maintenance cuts should be infrequent, perhaps every three to four weeks, and should adhere to the one-third rule, removing no more than a third of the blade length. This situational mowing helps prevent the turf from entering winter at a height that encourages matting and disease. This period is an opportune time to use the mower to mulch fallen leaves, chopping them into fine pieces that decompose quickly and return organic matter to the soil surface. This practice helps keep the lawn surface clear without the risk of damaging a frozen lawn with a rake.