When planting a new lawn, timing is one of the most critical elements of both seeding and aftercare. Once you've passed the hurdles of soil preparation, sowing the lawn seed and ensuring even and continuous watering, make sure you mow the grass at the appropriate times to enhance lawn establishment. The last thing you want to do is jeopardise your lawn project when you're so close to the finish line.
Generally, allow the newly seeded grass to grow to the maximum growing height recommended for its species. This can vary widely depending on the species. For example, let tall grasses grow to 10 cm (4 inches) before trimming and allow shorter varieties to grow to 5 cm (2 inches). It may take two months or more before your seeded grass reaches the appropriate heights for the first mowing.
Your newly seeded lawn reacts more sensitively to environmental factors, especially when it undergoes the stress of its first mowing. Avoid giving your lawn its first trim until the top layer of soil has dried out from rain or watering. Otherwise, the pressure of the lawnmower's weight will compact the underlying moist dirt and crush the developing roots.
When giving the grass its first cut, set your mower blades to a height that's slightly higher -- 6.5 mm (1/4 inch) -- than the maximum mowing height for its species. For example, a first mowing should reduce the grass to just above the recommended height. This helps minimise the stress of that first trim. If you've let your newly seeded grass grow exceptionally tall, keep in mind that grass should never have more than a third of its total length removed in a single cutting.
Wait three or four days, then give the new grass its follow-up mowing. At this time, lower your mower blades and bring the grass down to its actual recommended mowing height. After this second mowing, start a regular mowing schedule that allows the grass to reach its maximum growing height before being cut down to its recommended mowing height.