Mowing grass does help it grow, but not in the way one might expect. When performed correctly, cutting the grass blades fundamentally changes the plant’s growth habits rather than making the grass taller. Removing the top portion sends a biological signal that redirects the grass’s energy. This redirection shifts the focus from vertical growth to horizontal and lateral development, resulting in a denser, healthier turf.
How Mowing Encourages Lateral Growth
The upward growth of a grass plant is controlled by a phenomenon known as apical dominance. In an uncut grass shoot, the primary growing point, or apical meristem, produces hormones that suppress the growth of buds located lower down on the plant. This hormonal suppression ensures the main stem grows vertically toward the sunlight.
When the lawnmower blade removes the tip of the grass, the source of these growth-suppressing hormones is eliminated. This removal releases the lower, dormant buds from inhibition, prompting them to activate. The plant then focuses its energy on producing new side shoots, a process called tillering.
The result of increased tillering is a significant boost in the number of individual grass plants per square foot, which creates a thicker, carpet-like turf. This lateral growth pattern is an adaptive response that grasses evolved over millions of years to withstand grazing animals and fire. Regular, controlled mowing mimics this natural defoliation, encouraging the grass to grow outward rather than simply upward, thereby improving turf density.
Maintaining Optimal Mowing Height and Frequency
Achieving the benefits of lateral growth depends entirely on not removing too much of the leaf blade at one time. Turf experts recommend adhering to the “one-third rule,” meaning you should never cut off more than one-third of the grass blade’s total height during any single mowing session. For instance, if you want a final height of three inches, you should mow when the grass reaches a maximum of four and a half inches.
This practice is important because the grass blade acts as the plant’s food factory through photosynthesis. Removing more than one-third of the blade severely limits the plant’s ability to produce the energy it needs to sustain itself and grow new roots. When enough leaf area remains, the grass can continue to photosynthesize efficiently, minimizing stress and allowing energy to be directed toward strengthening the root system.
Taller grass blades naturally promote deeper root growth, which allows the plant to access water and nutrients more effectively. The increased height also shades the soil, which helps to retain moisture and keep the ground temperature cooler during warm periods, improving the lawn’s resilience against drought. Adherence to the one-third rule dictates mowing frequency, often requiring more frequent cuts during peak growing seasons to maintain the optimal height.
Mowing Practices That Damage the Lawn
Cutting the grass too short, a mistake often referred to as scalping, reverses all the benefits of proper mowing. Scalping removes too much of the photosynthetic surface, which starves the plant of energy and forces it to draw on stored reserves, severely stressing the roots. This practice can damage the crown of the grass plant, inhibiting its ability to grow and leaving the soil exposed.
The exposed soil and weakened turf create an opportunity for weed seeds to germinate and establish themselves. Furthermore, a severely cut lawn is vulnerable to disease and pests because the plant lacks the energy reserves to mount an adequate defense. Scalping is particularly damaging during hot weather, as the lack of blade height offers no shading protection to the soil and roots.
The condition of the mower blade itself also plays a significant role in turf health. A dull blade does not cut the grass cleanly; instead, it tears and shreds the leaf tips. These ragged, torn ends turn brown, giving the lawn a dried-out appearance, and create an open entry point for disease-causing organisms. Mowing wet grass should also be avoided, as the moisture causes clippings to clump together on the lawn surface, potentially smothering the grass beneath.