One-Third Rule

A rule of thumb used in mowing whereby the length of grass removed per cut is no more than one-third of the height of the grass. For example, if the grass height is measured as 30mm, then no more than 10mm will be removed during a mowing session: The height of cut would therefore be no less than 20mm. Removing excessive amounts of grass per cut will weaken a sward, thinning it and reducing root depth.