The safety of cutting grass in winter depends entirely on your specific climate and the biological state of your turf. For most homeowners, the winter season marks a period of rest for the lawn. However, in regions with mild winters, certain grasses may continue to grow, requiring occasional maintenance. Understanding the difference between a dormant lawn and one experiencing slow growth is essential to prevent severe damage. The decision to mow must be made carefully, considering temperature, moisture, and the grass’s vulnerability to physical stress.
Understanding Grass Dormancy
Turfgrass enters dormancy to survive environmental stress, such as cold temperatures, lack of light, or drought. This biological survival mechanism shuts down visible blade growth to conserve energy within the root system and the crown, the plant’s growth point located just above the soil line. Warm-season grasses (e.g., Bermuda or Zoysia) go dormant and turn brown when soil temperatures consistently drop below 50 to 55 degrees Fahrenheit.
Cool-season grasses (e.g., Kentucky Bluegrass and Fescue) slow their growth significantly below 40 to 45 degrees Fahrenheit. These varieties can sustain some growth during mild winter spells because they utilize C3 photosynthesis, which is efficient in cooler conditions. Activity during dormancy risks compromising the stored energy needed for a healthy spring green-up.
When and How to Mow in Mild Winter Conditions
Occasional mowing is possible for cool-season grasses that continue to grow during a mild winter, provided conditions are suitable. Only consider mowing when the air temperature has been consistently above 40 degrees Fahrenheit for several days, indicating active growth. Ensure the grass blades are completely dry and the ground is not frozen before starting the mower, as mowing wet or frozen grass causes tearing and significant damage.
If a cut is necessary, the goal is to remove only a small amount of growth without causing stress. Always adhere to the “Rule of a Third,” never removing more than one-third of the grass blade’s total height in a single session. Set the mower deck to the upper limit of the recommended height, typically maintaining blades between 2 to 2.5 inches. This higher cut allows the grass to photosynthesize, protects the crown from harsh temperatures, and reduces the likelihood of winter diseases.
Avoiding Damage to Frozen or Dormant Turf
The greatest risk to a winter lawn comes from activity on turf that is frozen, frosted, or fully dormant. When the grass blades are frozen, the water inside the plant cells crystallizes, making the tissue extremely brittle. Applying pressure from a mower or even footsteps can cause the frozen blades to physically shatter, leading to immediate cellular damage. This injury often appears as brown or black streaks that will not recover until new growth begins in the spring.
The pressure from a mower or foot traffic also impacts the soil structure, especially when the ground is frozen or partially thawed. This activity can cause soil compaction, pressing the soil particles together and reducing the pore space necessary for air and water to reach the roots.
Damage to the plant’s crown, combined with compacted soil, hinders the plant’s ability to resprout. Furthermore, cutting or stressing a dormant lawn can create entry points for cold-weather fungal diseases, such as snow mold, which thrive on injured or overly long grass under snow cover.