What Is The 1/3 Rule For Mowing?

While many homeowners opt to let a local yard crew do the work for them, for some, mowing and maintaining the lawn is a nearly sacred task that has lovingly been passed down through the generations. Of course, even the members of that latter category will likely have some pretty serious divergences when it comes to not only the right tools to use in maintaining your lawn, but the right methods as well.

Brand loyalty may ultimately come into play regarding the tools, as numerous manufacturers have lawn mowers available for purchase. Once you've selected the right mower, however, the question becomes how you set about using it on your grass. That question covers more than just how you want to line-out the yard, as the length at which you cut the grass may prove more important. 

Just in case you didn't realize, there are various settings on your lawn mower that allow you to adjust how short you cut the grass each time out. If you're uncertain which of those settings to use when cutting your own lawn, some claim the "1/3 rule" is one worth following. As you've likely surmised, that rule dictates that you should not cut more than 1/3 of the grass's height each time you mow. It was reportedly also established after a lengthy study by the U.S. Department of Agriculture, by the way, so it's more legit than you might think. Here's what else you need to know about the 1/3 mowing rule.

Keeping to the 1/3 rule for mowing your lawn may start with selecting the correct height setting on your mower, but there's more to the matter than that. According to purveyors of the method, the length of the grass itself must also be taken into account. As the rule goes, the grass should not be cut unless it's grown at least 50% taller than its ideal height. From there, cut only 1/3 of the grass blade, meaning that if the grass is 3-inches tall, you should cut only 1-inch off the top.

As noted, there is science behind the method, with a professor of Turfgrass Management confirming to Lawn Love that adhering to the 1/3 rule can, "help prevent (shock) when a significant amount of top growth is removed at once," adding that mowing the grass too short, "often cuts into the stem of the plant, rather than just leaf material." 

Not cutting the grass so short that such a "shock" sets in will ensure that the process of photosynthesis – in which plants and grass use sunlight, water, and gases to make their own food — can continue, keeping the grass itself alive and healthy. It also ensures that grass can properly continue to absorb necessary minerals such as nitrogen, phosphorus and potassium, among others. To that end, it's recommended that you not bag your clippings when practicing the 1/3 rule for mowing, as the mulched grass shavings can act as a sort of natural fertilizer for the lawn as it decomposes. The same logic may also apply to unraked leaves, by the way.