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How high should I cut my grass in the summer?

August 2nd, 2019 by Tuff Turf Molebusters
Mowing
Mowing the grass too low is the biggest mistake we see people make.  No matter how many times we recommend mowing at the highest setting during the middle of the summer, many people still mow the grass too short.  I have heard that mowing higher means mowing more frequently.  This is completely wrong, in fact the opposite is true.  The rule of thumb is to never cut off more than 1/3 of the blade of grass at one time.  If you apply the 1/3 rule and always let your grass grow long enough to cut 1/3 off, you can see in the chart below that raising the mowing height from 2″ to 4″ also doubles the number of days between mowings.
I realize that letting your grass get 6″ high before mowing is long and covers your shoes when you walk through it.  It looks like it needs to be mowed when you just finished mowing.  However, longer grass will remain green longer in the heat, have less weeds, and less pressure from diseases.  Keep in mind that this is for a short time period when we are in the middle of summer and have temperatures above 80 every day.
Besides for appearance, lawns are cut too short because most home-owner mowers can’t mow higher than 3″.  The small, mowing only companies don’t understand the agronomics of mowing high, and certainly don’t like to be told how to do their job when asked to raise their mower.  We just witnessed this last week at a turf tour where a MSU professor asked a group of Grand Rapids lawn care professionals how high to mow in the summer.  All the fertilizing companies said 3.5″ – 4″, while the companies that only mow said 2.5″ – 3″.
The depth of the roots of grass are a direct proportion to the height it is mowed