Mowing too early or too late can stress young grass, stunt growth, or even damage the delicate root systems. This guide explores the key factors to consider, including grass height, growth stage, and environmental conditions, to help you determine the perfect time for that first cut.
When to Mow New Grass
For new grass, wait until it reaches 3 to 4 inches in height before mowing, typically 4 to 6 weeks after germination for seeded lawns or 2 to 3 weeks for sod. This height ensures strong roots and enough leaf surface for photosynthesis.
Check root development by gently tugging blades (seeded) or lifting sod corners to confirm anchoring. Mow on a dry, mild day (60°F to 80°F) to avoid stress, using sharp blades set to cut only the top third of the grass to prevent tearing or compacting soil.
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Grass Height: The Primary Indicator
Grass height is the most reliable indicator of when to mow. Most experts recommend waiting until new grass reaches a height of 3 to 4 inches before the first cut. This height ensures the grass has developed a strong root system and enough leaf surface to support photosynthesis, which fuels growth. Here’s a breakdown by grass type:
- Cool-season grasses (e.g., Kentucky bluegrass, tall fescue, perennial ryegrass): Mow when the grass reaches 3 to 3.5 inches.
- Warm-season grasses (e.g., Bermuda, Zoysia, St. Augustine): Mow when the grass hits 2.5 to 3 inches, as these varieties thrive at slightly shorter heights.
For seeded lawns, this height is typically reached 4 to 6 weeks after germination, depending on the grass type and growing conditions. Sod may reach this height in 2 to 3 weeks, assuming proper rooting.
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Checking Root Development
Before mowing, ensure the grass has a solid root system. For seeded lawns, gently tug on a few blades; if they resist, the roots are likely established. For sod, lift a corner to check if roots have anchored into the soil.
If the sod lifts easily, wait another few days and water consistently to encourage rooting. Mowing before the roots are secure can cause the grass to shift or tear, leading to uneven patches.
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Environmental and Weather Considerations
Weather plays a significant role in determining when to mow new grass. Avoid mowing during extreme heat, drought, or heavy rain, as these conditions stress young grass. The ideal time is a dry, mild day with temperatures between 60°F and 80°F.
Wet grass clumps under the mower, leading to uneven cuts and potential fungal issues. If you’re in a region with distinct seasons, aim to mow in early morning or late afternoon to avoid midday heat.
Soil moisture is another factor. New grass needs consistent watering (about 1 inch per week), but the soil should be firm. Angling the blade at a slight upward angle (about 10 degrees) helps prevent tearing and promotes cleaner cuts on delicate grass.
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Post-Mowing Care
After the first mow, continue nurturing your lawn. Water lightly to keep the soil moist but not soggy, and avoid heavy foot traffic for another week or two.
Apply a starter fertilizer with nitrogen and phosphorus to encourage growth, following package instructions to avoid over-fertilizing. Monitor the lawn for weeds, which can emerge quickly in new lawns, and address them promptly with spot treatments or hand-pulling.
Final words
Mowing new grass at the right time, when it’s 3 to 4 inches tall, well-rooted, and under favorable weather conditions, sets the foundation for a healthy, vibrant lawn.
By using sharp blades, mowing at the correct height, and following up with proper care, you’ll help your grass thrive. Patience and attention to detail during these early stages will reward you with a lush, durable lawn that enhances your outdoor space for years to come.
