Turfgrass Establishment Series – Mowing
By Pam Sherratt
If the growing conditions after seeding have been favorable, the new grass can be mowed for the first time four to six weeks after seeding. This window is shorter for highly-managed, irrigated turf, and longer if the conditions have been challenging (e.g. droughty). The grass should be 3-4 inches tall with good density.
The first mow is done with a rotary mower when the grass reaches a height one-third higher than the regular mowing height. For example, if a 3-inch height is desired, mow when the grass is at 4 inches. This adheres to the one-third rule of mowing where no more than one-third of the leaf tissue is removed. This is because mowing is a stress to turf as the grass needs its leaves to capture and store energy. The ideal height for lawns in Ohio is 3-4 inches. Shorter lawns will be stressed, have shallow root systems and be less likely to compete with weeds. Longer, and the lawn will lose density because the growing part of the turf (the base) is shaded. If mowing has not taken place regularly because of rain and the grass is too long, mow the grass higher than normal and gradually bring the height back down to the desired height. Check the mowing height of the mower by measuring between the base of the grass plant and the bottom of the mower deck (Image 1).
Mowing encourages the grass to tiller, with new shoots sprouting from the base of the turf plant resulting in a thicker, denser lawn. Mowing at least once per week, twice in spring and fall, is a standard approach. If the lawn is a mixed species sward, frequent mowing will help to mask differences in plant height and texture (Image 2).
Mowing more frequently will aid establishment (tillering) but must be based on surface conditions. If there is still bare soil visible and the ground is wet, the mower wheels can cause ruts and other surface damage. If conditions are too dry, the grass may be overtly stressed after the operation. If a large amount of clippings are produced after the first mow and the mower does not mulch them, set the mower height high, and run over them when they are dry, with the blade running to disperse the clippings, or rake them up and add them to the compost bin (Image 3). With subsequent mowings, return clippings to your lawn to reduce fertilizer applications. A mower with a mulching setting can be used to leave behind finely-shredded clippings.
It’s important to keep the mower blades sharp and clean. Typically, blades should be sharpened after 25 hours of use (two times per season). Changing the direction of cut each time will prevent the grass from laying over in one direction. Use caution when mowing bumpy ground to avoid scalping. Overlap each run to make sure there are no missed strips of grass, and finish the job by trimming/edging, to create crisp clean edges.