When the summer sun beats down, many homeowners face the dilemma of whether to cut their lawn short for a tidy appearance or leave it long for health. Mowing short to reduce frequency can actually be detrimental to the turf’s survival during periods of high heat and drought. Scientific evidence supports raising the cutting height in warm weather to encourage deeper roots, manage soil temperature, and conserve water. Understanding the biological and physical reasons behind this recommendation can transform a struggling summer lawn into a resilient one.
How Cutting Height Affects Root Growth
The length of the grass blade maintains a direct relationship with the depth and density of the root system beneath the soil. Turfgrass plants prioritize energy generated through photosynthesis, which occurs in the leaves. When a large percentage of leaf tissue is removed during a short cut, the plant immediately directs stored energy toward replacing the lost photosynthetic surface area. This regeneration comes at the expense of root maintenance and growth.
Consistently short mowing results in a shallow root system, making the plant less capable of accessing moisture and nutrients when the surface soil dries out. In contrast, a longer blade allows for greater photosynthesis, providing the surplus energy needed to maintain a deep root network essential for surviving summer stress.
Soil Shading and Evaporation Control
A taller grass canopy shades the soil surface from direct solar radiation. This shade reduces the heat reaching the ground, keeping the soil cooler. Cooler soil temperatures decrease the rate of water loss through evaporation. The dense canopy also lowers evapotranspiration by slowing air movement and trapping moisture near the surface. This moisture conservation reduces the frequency and volume of irrigation needed during a heatwave.
Temperature Management in Turf
Beyond water conservation, increased turf height acts as insulation, providing thermal protection for the plant. Short grass exposes the soil and the plant’s crown—the growing point—directly to intense heat. This exposure leads to higher soil temperatures, inhibiting root function and causing heat stress. A longer canopy maintains a cooler microclimate, shielding the crown and upper soil profile from damaging temperatures. Keeping the soil and crown cooler allows physiological processes, such as nutrient and water uptake, to function more efficiently.
Adjusting Mowing Strategy for Summer
To capitalize on these benefits, homeowners should raise the mower deck at the start of the warm season. For cool-season grasses, such as Kentucky bluegrass or tall fescue, the summer cutting height should be set between 3 and 4 inches. Warm-season grasses, like Bermuda or Zoysia, benefit from heights in the 2 to 2.5-inch range.
Adhere to the “one-third rule,” which states that no more than one-third of the total blade length should be removed in a single mowing session. This rule may require more frequent mowing, but it prevents the plant from going into shock and wasting energy reserves. Always ensure the mower blade is sharpened, as a dull blade tears the grass, creating wounds that lose moisture rapidly and increase disease susceptibility.