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Ask a Master Gardener: How to mow an overgrown lawn

Lawn care experts at Extension recommend to never cut grass by more than one-third of the length of the grass blade.

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Q: I’m participating in "No-Mow May" to help pollinators. The idea is to let some early-flowering weeds grow to provide food for pollinators when not much is blooming yet. The grass is getting long. Once I start mowing again, will it hurt the lawn to cut it back to its regular height all at once?

A: You’re right to be cautious.

Lawn care experts at Extension recommend that we never cut our grass by more than one-third of the length of the grass blade. Cutting more in a single mowing can damage your lawn. It needs those green parts to photosynthesize and send energy to the roots, and cutting too much at once makes that process more difficult. Mowing a lawn that has become overgrown back to its regular length in one fell swoop can lead to unattractive brown patches in the lawn.

So what should you do if your lawn gets too long while you’re away on vacation or because it’s too wet to mow or because you’re helping pollinators in early spring?

The best thing to do is to set your mower blade high and remove only one-third of the blade of grass, give it a few days to recover, and then mow again, setting the blade a bit lower.

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Mowing
Jamie Buchite, of Duluth, man-powers his lawnmower up a steep hill in his front yard in 2017. The University of Minnesota Extension recommends never cutting grass by more than one-third of the length of the grass blade.
Bob King / File / Duluth News Tribune

In general, it’s better for your lawn to keep your turfgrass on the longer side than to cut it putting-green short. Longer grass helps shade out weeds, and it gives the plant more to work with when it comes to photosynthesis.

You can have a short lawn if that’s what you need for some specific purpose, such as putting practice, but it’ll require more fertilizer and more weed control. Short grass also requires more frequent mowing, because you still only want to remove 1/3 or less of the blade at a time.

We recommend leaving the grass clippings on your lawn rather than bagging them up. They add nitrogen to your soil and reduce the need for fertilizer. This is another reason not to cut a lot of the grass blade at once. You don’t want to smother the lawn with thick mats of clippings, and you don’t want to have to do pass after pass with the mower to cut up the long clippings.

Written by U of M Extension Master Gardeners in St. Louis County. Send questions to  features@duluthnews.com .

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