Mowing a lawn during summer heat stresses both the turfgrass and the operator. Turfgrass begins to suffer from heat stress when temperatures rise above 85°F, requiring a shift in routine to protect the lawn’s health. The core dilemma is minimizing shock to the grass while safeguarding the operator from heat-related illness. Understanding the physiological effects of high temperatures is the first step in deciding how to proceed with mowing.
How Heat Stress Affects Grass Health
Mowing grass struggling with heat inflicts a physical wound on the plant. This cut surface immediately accelerates the rate of water loss, known as transpiration, when the grass is already struggling to retain moisture. Removing the leaf tissue forces the plant to expend energy on healing rather than surviving the heat.
High air and soil temperatures inhibit the growth of grass roots. When roots are shallow, they have a limited capacity to absorb the water and nutrients needed to recover from mowing. This energy imbalance, where the plant uses more energy for respiration than it produces, pushes the turf toward a weakened state.
In response to sustained heat and drought, many cool-season grasses enter a protective dormancy, turning brown to conserve resources. Mowing a lawn in this dormant state is discouraged because the activity can damage the plant crowns, which are the points where new growth emerges. The stress of a fresh cut creates an entry point for fungal pathogens that thrive in warm, humid conditions. Diseases such as Brown Patch and Dollar Spot frequently take hold on heat-stressed turf, resulting in discolored or dead patches.
Adjusting Mowing Strategy for High Temperatures
The optimal time to mow in hot weather is during the cooler parts of the day, specifically early morning after the dew has dried or in the early evening. Avoiding the hottest period, typically between 11 a.m. and 4 p.m., minimizes the immediate shock and desiccation stress placed on the grass blades. If the lawn shows signs of wilting, such as footprints remaining visible, mowing should be postponed until the turf recovers.
The single most effective adjustment is to raise the mower’s cutting deck significantly, often to 3 to 4 inches or the highest setting. Taller grass blades provide shade for the soil, which helps keep the roots cooler and substantially slows moisture evaporation. Adhering to the “one-third rule” is especially important when the grass is stressed; never remove more than one-third of the total blade height per mow.
Using a sharp blade is necessary during heat stress, as a dull edge tears the grass, creating a wound that requires more energy to heal and loses more water. Mulching the clippings back into the lawn is beneficial because they quickly decompose, returning moisture and nutrients to the soil. During prolonged heat waves, reduce the frequency of mowing, as the turf’s growth rate naturally slows.
Safety Guidelines for Mowing in the Heat
Prioritizing personal safety is crucial when mowing in hot weather. Hydration is paramount, requiring the operator to drink water before, during, and immediately after working, even if thirst is not felt. This fluid intake helps the body regulate its core temperature and prevent overheating.
Wearing appropriate clothing offers protection. Loose-fitting, light-colored clothing made from breathable fabrics like cotton or moisture-wicking synthetics helps reflect sunlight and allows air to circulate, aiding sweat evaporation. A wide-brimmed hat and sunscreen with an SPF of 30 or higher should be used to guard against the sun’s ultraviolet radiation.
Operators must be vigilant for signs of heat-related illness, which can escalate quickly. Symptoms of heat exhaustion include heavy sweating, dizziness, nausea, and muscle cramps. If these signs appear, work must stop immediately, and the operator should move to a cool, shaded area. Mower maintenance is also part of heat safety; ensuring the engine’s cooling fins are clear of debris and the air filter is clean prevents the equipment from overheating.