Mulching a lawn with grass clippings involves allowing the finely chopped organic material to fall back onto the soil surface during mowing. This practice, often called “grasscycling,” returns nutrients, primarily nitrogen, phosphorus, and potassium, back to the soil, acting as a natural, slow-release fertilizer. Clippings are composed of about 85% water, which also aids in retaining soil moisture and enhancing turf health.
The Continuous Mulching Schedule
The most effective schedule for mulching is to do it every time the lawn is mowed during the active growing season. This frequency is governed by the grass’s growth rate, which changes depending on the season and climate conditions.
The schedule is dictated by the “one-third rule,” which states that you should never remove more than one-third of the grass blade’s height in a single mowing session. This rule minimizes stress on the grass and ensures the clippings are small enough to decompose quickly and filter down to the soil. For example, if you maintain a lawn height of three inches, you must mow when the grass reaches four and a half inches.
During the vigorous growth of spring, this rule may require mowing every four to five days. As growth slows in the heat of summer or cooler autumn temperatures, the frequency can decrease to every seven to ten days. The schedule is responsive to how quickly the grass is growing to maintain the health benefits of finely mulched material.
Proper Technique for Effective Mulching
Achieving the desired fine particle size depends heavily on the proper mechanical execution of the cut. The ideal setup involves using a dedicated mulching mower or installing a specific mulching kit, which includes special blades and a deck plug. This setup keeps the clippings circulating under the deck, allowing the grass to be cut multiple times before being forced down into the turf canopy.
The sharpness of the mower blade is an important factor, as a dull blade tears the grass instead of cleanly cutting it, stressing the plant and creating entry points for disease. Sharp blades ensure the clippings are finely pulverized, which is necessary for rapid microbial breakdown and nutrient cycling. The resulting small particles must settle quickly below the grass blades to avoid smothering the turf.
The mower deck height must be set according to the one-third rule to prevent the machine from becoming overwhelmed and leaving behind clumps. Mowing patterns should incorporate overlapping passes to ensure the clippings are evenly distributed. A uniform distribution allows the organic material to decompose efficiently, feeding the lawn without creating a noticeable layer on the surface.
Conditions That Require Stopping or Adjusting Mulching
While continuous mulching is recommended for turf health, several conditions require temporarily switching to bagging the clippings.
Lawn Disease
One exception is the presence of lawn disease, such as rust or fungal spots. Mulching diseased clippings can spread fungal spores across the entire lawn, worsening the infection.
Excessive Moisture
Mulching should also be avoided when the grass is excessively wet, such as after heavy rain or morning dew. Wet clippings are heavy and tend to clump together, sticking to the mower deck and falling onto the lawn in thick patches. These large clumps can smother the turf and inhibit light and air penetration, leading to yellowing or dead spots.
Overgrown Grass
If the grass has violated the one-third rule by growing too long, the resulting volume of clippings will be too substantial for the soil to process quickly. Leaving a large amount of long clippings creates a thick layer that can lead to turf smothering and contribute to a thatch problem. In this scenario, it is better to bag the excess material or make multiple passes over several days to gradually remove the height.
Weeds Gone to Seed
If the lawn contains an abundance of weeds that have gone to seed, bagging the clippings is advisable. This prevents the viable seeds from being redistributed across the lawn during mowing. Collecting and disposing of these seed heads helps reduce the weed population in subsequent seasons.