The timing of the first lawn mowing of the year is more a function of biological and environmental readiness than a date on the calendar. Mowing too early can cause significant stress to the newly awakened grass plants, potentially leading to a weakened lawn throughout the season. The decision to cut should be based on the grass height, soil conditions, and temperature, all of which indicate the lawn is actively growing and healthy enough to recover from the stress of mowing.
Timing the First Cut Based on Grass Height
The primary indicator that the lawn is ready for its first cut is the height of the grass blades, signaling active growth. Most experts suggest waiting until the grass reaches a height of about three to four inches before starting the mower. While the ideal growth height will vary depending on your specific grass type, the principle is rooted in the plant’s biology. Cool-season grasses, such as fescue or perennial ryegrass, are generally the first to green up and enter their growth phase in early spring.
The most important rule to follow for the first mow, and all subsequent cuts, is the “One-Third Rule.” This rule dictates that you should never remove more than one-third of the grass blade’s total height in a single mowing session. If your target height is three inches, for example, you should mow when the grass reaches a maximum of four and a half inches. Violating this rule, especially during the first cut, severely shocks the plant by removing too much photosynthetic surface area.
Removing excessive leaf tissue forces the grass to pull energy reserves from its roots for recovery, which hinders deep root development. Healthy root systems are the foundation for drought and heat resistance later in the summer, so this early shock weakens the lawn’s long-term resilience. If the grass is significantly overgrown, cut it down gradually over several days, adhering to the one-third rule each time, rather than scalping it all at once.
Checking Soil and Temperature Conditions
Beyond the height of the grass blades, you must confirm that the underlying environmental conditions are suitable for mowing. The most significant non-plant factor is the moisture level of the soil, as mowing when the ground is saturated can be highly damaging. The weight of the mower and the operator on wet soil causes soil compaction, which squeezes the air pockets out of the ground.
Compacted soil restricts the flow of oxygen, water, and nutrients to the grass roots, slowing growth and eventually leading to thin or patchy areas. A simple test for soil readiness is the “footprint test”: if your footprints remain clearly visible after walking across the lawn, the soil is too wet, and you should wait for it to dry. Mowing wet grass also results in uneven cuts because the blades bend over, and clippings clump together, which can smother the grass underneath.
The soil temperature must also indicate that the roots are metabolically active and ready to support new growth. While air temperature fluctuates quickly, soil temperature changes slowly and is the true driver of spring growth. For most cool-season grasses, active growth requires the soil at a depth of a few inches to consistently exceed 40°F. Waiting for these consistent temperatures ensures the plant can dedicate energy to recovery and growth after the initial cut.
Proper Mower Settings for the Initial Mow
Once the grass height and environmental conditions are right, the execution of the first cut requires specific attention to equipment settings. The most important preparation is ensuring the mower blade is sharp, as a dull blade tears the grass instead of cleanly slicing it. Torn grass blades leave ragged, white or brown tips, which look unsightly and create a larger wound on the plant, making it more susceptible to disease and pests.
Sharpen the blade at least once per season, ideally before the first cut, to ensure a clean, quick-healing cut. For the initial spring mow, the cutting deck should be set higher than the height used during the summer months. Mowing higher helps shade the soil, keeping it cooler and retaining moisture, which benefits the developing root system. For cool-season grasses, setting the mower to the highest available setting, often three inches or more, is common practice.
If the grass is very tall from winter dormancy or contains significant old debris, bag the clippings during the first pass. If you adhered to the one-third rule, mulching the clippings is beneficial. Finely chopped clippings return water and nutrients to the soil, acting as a natural fertilizer.