The common belief that cutting grass makes it spread is not entirely accurate, but it captures the result of a precise biological process. Mowing triggers a mechanism that leads to increased density and thickness, rather than causing plants to physically move. This process, known as tillering, is the plant’s natural response to the removal of its upper growth, which creates a lush turf. Understanding the internal structure of the grass plant reveals how this mechanical action produces such a change.
Understanding the Grass Plant Structure
The grass plant’s ability to survive repeated cutting is due to the unique location of its growth points. Unlike many other plants, the grass plant has a structure called the crown, which sits safely near the soil surface. The crown is the compressed base of the plant, acting as the connecting tissue between the roots and the shoots.
The crown is a hub for active cell division, containing meristems and small, dormant buds known as latent buds. Vertical growth comes from the terminal bud, which is responsible for pushing the leaf blades upward. Because the growth zone is low to the ground, mowing removes only the leaf tips, leaving the crown and latent buds undamaged and ready to initiate new growth.
The Biological Trigger for Lateral Growth
The phenomenon that links mowing to a thicker lawn is called apical dominance, a physiological control system found in many plants. The terminal bud, which is the uppermost growing point on the shoot, produces a growth hormone called auxin. This auxin travels downward, effectively suppressing the growth of the latent buds clustered in the crown area.
When the mower removes the top portion of the grass blade, it also removes the source of the growth-inhibiting auxin hormone. With the suppression lifted, the latent buds are chemically signaled to become active. They begin to grow laterally, developing into new vertical shoots called tillers. Tillering is the biological process where a single grass plant multiplies itself into a dense cluster of shoots, increasing the overall thickness of the turf.
Spreading Mechanisms of Common Turf Grasses
While tillering creates density in nearly all turf grasses, some types possess additional structures that allow for genuine horizontal expansion. These specialized stems are distinct from the vertical tillers that emerge from the crown and are designed for vegetative propagation.
Stolon
One type of spreading stem is the stolon, which grows horizontally above the soil surface, forming new plants at its nodes. Grasses such as St. Augustine and Centipede grass rely on these runners to creep across the ground and establish new roots.
Rhizome
The second type is the rhizome, a modified stem that grows horizontally underground. It also produces new shoots and roots from its nodes. Kentucky bluegrass and Zoysia grass utilize these underground stems, which store energy and allow the plant to spread aggressively beneath the surface.
Mowing Techniques to Maximize Thickness
To translate this biological understanding into a thicker lawn, specific mowing techniques must be consistently applied. The most important rule to follow is the “one-third rule,” which states that you should never remove more than one-third of the grass blade’s total height in a single mowing. For example, if your grass is four inches tall, you should cut no more than about 1.3 inches, leaving 2.7 inches of blade remaining.
Adhering to this rule prevents undue stress on the plant, ensuring that enough leaf surface remains for efficient photosynthesis and root development. When grass is cut too severely, known as scalping, the plant must divert energy away from tillering and root growth to repair the damage.
Maintaining a taller cutting height, typically between 2.5 and 4 inches for most turf varieties, promotes deeper root systems. This height also allows the grass to shade out weed seeds, further encouraging a dense turf. Finally, using a sharp mower blade is important, as a clean cut minimizes the wound on the leaf. This allows the plant to quickly recover and focus its resources on activating those lateral buds for increased thickness.