In an ideal world, as soon as the lawn reached an appropriate height, we’d get out the mower, remove one third of that height according to the one third rule, and wait for it to return to mowing height again. Unfortunately, Mother Nature is just a tad more variable than that!

What typically happens is the lawn reaches a height half again taller than we ever intended, leaving us to try and figure out what height we should be at now! Fortunately, there is at least a little flexibility when it comes to mowing height!

If a consistent one third removal can’t be attained, you are probably best to set your mower as high as possible and bring it down in steps to an appropriate height. You might well cut off more than a third of the grass blade height, but mowing more often and bringing the height down gradually until you reach your target height is probably the best option for the turf.

Mowing height is important because of the way grass plants respond to removal. When a grass plant grows, it does so from stored energy in roots until it has enough leaves to support energy production that replenishes root reserves. If you remove too much leaf area, the plant reacts by pulling stored energy reserves from roots to quickly send up new growth. That may work fine until insect or disease or drought stress kicks in. If the plant has too few energy reserves when stress hits, the grass will likely not respond well and the stand can start to thin.

While a good fertility and mowing program often helps combat these issues, continued removal that results in thinning can quickly lead to weed pressure and other cultural issues that become very difficult to stay ahead of – particularly if the one third rule continues to be exceeded. For best results, always return to the one third removal rule. A thick, healthy stand will in many cases take care of weed issues by itself. Mowing management is a big part of encouraging that healthy stand.