How Long Should I Cut My Grass

Air Temperature
Here in Michigan, most of our lawns are made up of a blend of cool season grasses like kentucky bluegrass, creeping red fescue and perennial ryegrass. The sweet spot for cool season grasses to thrive is 50-80 degrees. This temperature range usually occurs in the spring and fall. That’s why we see our lawns grow so fast in the spring and fall. In the summer, when air temperature can be above this range for a duration of time, lawns can struggle and even go into summer dormancy; especially unirrigated lawns. Dormancy is a protective mechanism that allows grass to survive during these harsh, dry conditions. During extended amounts of high temps with no precipitation (or irrigation), dormant lawns will continue to lose moisture from the crown and could eventually die. When air temperature is high, soil temperature increases. When the soil temperatures increase, it begins to dry out and loses valuable nutrients. Grass roots are what feed the grass. In order for the roots to consume the nutrients, the soil must have moisture, while the grass needs a good root system.

Root Depth
Okay, so what does this do have to do with cutting height? Actually a lot. Mowing height is directly related to how deep the grass roots grow. As you can see in the diagram below, the longer the grass blade, the deeper the roots grow. Compared to short grass having shallow roots.

“The longer the grass blade, the deeper the roots grow. Compared to short grass having shallow roots.”

So now we know that short grass has a shallow root system. When the blade of the grass is shorter, it allows more sunlight to penetrate the soil, increasing soil temperature while stripping the nutrients out of the upper soil. Since short grass has a shallow root system and the upper soil is dry with less nutrients, the grass begins to go dormant much quicker. In comparison, longer grass blades will provide more shade, which in turn keeps the soil cooler. The deeper roots will be able to absorb more nutrients and provide more moisture to the grass.

What About Weeds?
Lets face it… Grass is high maintenance. It needs to be properly irrigated, prefers a 50-80 degree temperature range and needs to have the proper nutrients in the soil. Here’s the bad news, weeds thrive in poor soil conditions. They do not require as much water or nutrients to grow. So from the information we already know, short grass provides an ideal situation for weeds. Longer grass will keep the soil moist, protecting the grass and choking out weeds.

So How Long Should I Cut My Grass?

Ideally in Michigan you want to keep your grass between 3.5-4.0 inches. As a business owner, we have some clients say their lawn looks “messy” a couple days after it was mowed. I tell them my lawn is the same way… I remind them that even though my lawn may look “messy”, my lawn is also the healthiest on the block. My lawn has minimal amount of weeds (if any), has great color and with proper irrigation, never fall into dormancy. You also want to follow the 1/3 rule when cutting your lawn. Cutting more than 1/3 of the blade could weaken the grass causing the lawn to become more susceptible to heat stress, disease and weeds. It is much more important to cut your lawn based on grass growth than schedule dates. In spring months lawns may need to be cut 2 times a week compared to dry summer months when the grass grows at a much slower rate. Lastly, you do not want to ever cut your lawn very short so you don’t need to mow it as much. This creates so much stress on the grass.

Short vs Long
We now understand how grass blade length directly affects the root depth and soil temperature. If you follow these 3 steps, your lawn will thrive: