Leaving grass clippings on the lawn, a practice known as grasscycling or mulching, is generally a beneficial approach to lawn care. This technique saves time and effort by eliminating the need to bag and dispose of yard waste, and it offers an environmentally friendly way to manage your lawn. It is a simple method that returns organic material back into the soil, supporting a healthier turf ecosystem.
Natural Fertilization from Clippings
Grass clippings act as a natural, slow-release fertilizer, returning essential nutrients to the soil. They are composed primarily of water (approximately 80% to 85%), allowing them to decompose quickly once they settle onto the turf surface. This rapid breakdown releases compounds back into the soil, preventing the accumulation of material that could lead to thatch buildup.
A primary benefit of grasscycling is the nutrient return, particularly nitrogen, which promotes green, vigorous growth. Clippings typically contain about 4% nitrogen by dry weight, along with phosphorus and potassium. Leaving the clippings can reduce the need for synthetic nitrogen fertilizer by an estimated 15% to 25% annually. The decomposing material also feeds beneficial soil microbes, improving soil health and structure.
Mowing Height and Frequency Requirements
The success of leaving clippings on the lawn depends on employing proper mowing techniques. To ensure the clippings are small enough to filter down to the soil surface and decompose rapidly, you must adhere to the “one-third rule.” This rule states that you should never remove more than one-third of the grass blade’s total height in any single session. For example, if you maintain your lawn at 3 inches, you should mow when the grass reaches approximately 4.5 inches.
Following this principle often means increasing the frequency of mowing, especially during peak growth periods. Mowing more often ensures the clippings are short and manageable, preventing them from clumping and smothering the grass below. Mowing with a sharp blade is also important, as a dull edge tears the grass blade, stressing the plant and making it more susceptible to disease.
The ideal mowing height varies by grass type. It generally ranges from 2.5 to 4 inches for cool-season grasses like Kentucky bluegrass and tall fescue. Warm-season grasses, such as Bermuda or Zoysia, are often maintained at a shorter height, typically between 1 to 2.5 inches. Taller grass blades shade the soil, which helps retain moisture, suppress weed growth, and encourage deeper root development.
Situations Requiring Removal
While grasscycling is generally recommended, clippings should be removed in specific circumstances to protect the lawn’s health. The most common exception is when the volume of clippings is excessive, resulting in large, visible clumps on the turf surface. These heavy clumps block sunlight and trap moisture, smothering the grass blades underneath and leading to brown or dead patches. Excessive volume usually occurs when mowing has been delayed, such as after heavy rain or rapid growth.
A second situation requiring removal is when the lawn is showing signs of fungal disease, such as brown patch or dollar spot. Fungal pathogens reside on the grass blades, and leaving the infected clippings will spread disease spores across a wider area. In these cases, bagging and removing the infected clippings is necessary to prevent further contamination and promote turf recovery. Washing the mower deck is also necessary to contain the spread of the disease.