The frequency of cutting grass in the summer is rarely a fixed schedule, but depends entirely on the lawn’s growth rate and prevailing environmental conditions. Summer heat and drought cause growth to fluctuate significantly, requiring constant adaptation of the mowing routine. Understanding how grass reacts to being cut under heat stress is essential for maintaining a healthy lawn. Proper summer cuts protect the grass from damage and promote necessary deep root growth.
The Essential “One-Third Rule”
The true measure of mowing frequency is the “one-third rule,” not the calendar. This biological principle dictates that you should never remove more than one-third of the grass blade’s total height in a single cut. Adhering to this limit prevents the plant from going into shock, which is a major stressor during summer heat.
Removing too much leaf tissue severely limits the plant’s ability to perform photosynthesis, the process that converts sunlight into food. The grass needs sufficient leaf surface area to capture solar energy for survival. When more than one-third is removed, the plant must divert energy away from its root system to rapidly regenerate the lost blades.
This diversion of energy can inhibit root growth, leading to a shallow, weakened root structure. Shallow roots are less effective at accessing water and nutrients, making the lawn highly susceptible to drought and heat damage. For example, if the desired finished height is 3 inches, wait until the grass reaches 4.5 inches before mowing, removing only 1.5 inches of growth.
If the grass grows quickly, this rule may require mowing every four to five days instead of a standard seven-day schedule. Conversely, if growth slows dramatically during a drought, mowing might not be needed for ten days or more. Avoid mowing entirely if the grass has gone dormant and turned brown. The one-third rule determines when the grass is ready for its next cut, regardless of the day of the week.
Adapting Mowing Height for Summer Stress
While the one-third rule determines frequency, the actual height of the cut must be raised in the summer to mitigate heat and drought stress. Taller grass blades provide a natural canopy that shades the soil surface. This shading keeps the soil cooler and significantly reduces water evaporation, aiding in moisture retention.
For cool-season grasses, such as Kentucky bluegrass and fescues, which struggle in high temperatures, the recommended summer height is often between 3.5 to 4.5 inches. Maintaining this height encourages deeper, more robust root systems better equipped to withstand dryness. Taller, denser turf also helps suppress weed germination by blocking sunlight from reaching the soil.
Warm-season grasses, like Bermuda and Zoysia, thrive in the heat and are generally cut shorter than cool-season types. Even these species benefit from a slight increase in cutting height during peak summer stress, typically aiming for 1.5 to 3 inches. Cutting grass too short (scalping) exposes the plant’s crown and the soil to intense sunlight, leading to browning and increased vulnerability to disease. Raising the mowing deck by just half an inch provides considerable insulation and reduces moisture loss during the hottest weeks.
Optimizing Your Cut: Timing and Clipping Management
The time of day chosen for mowing plays a role in minimizing summer stress on the grass. The best time to cut is typically mid-morning, between 8 a.m. and 10 a.m., after the morning dew has evaporated. Mowing dry blades ensures a clean cut, as wet grass tends to tear or clump, leading to uneven results.
An alternative preferred time is the late afternoon or early evening, generally between 4 p.m. and 6 p.m., after the high heat of the day has passed. This timing allows the freshly cut tips several hours to recover before the evening dew settles. Mowing during the hottest part of the day (noon to 3 p.m.) forces the grass to recover under intense sun and heat, causing unnecessary stress.
Clipping management, often called “grasscycling,” is an effective summer practice that benefits the stressed lawn. Leaving the finely cut clippings allows them to quickly decompose, returning valuable nutrients, primarily nitrogen, and organic matter back to the soil. These clippings also act as a light mulch layer, helping to reduce water evaporation from the soil surface. Grasscycling can replace a portion of the lawn’s annual fertilizer needs and saves time by eliminating the need to bag and dispose of yard waste.