06/08/2017
Understanding the “1/3 Rule" of Mowing
It’s a well-known rule of thumb that you should never remove more than 1/3 of the height of your grass when mowing… but very few homeowners understand why.
So… What is the 1/3 rule?
The 1/3 rule is mowing removes the uppermost, green shoot growth of the grass. This is where photosynthesis occurs. Removing more than 1/3 of the shoot height will drastically decrease the rate of photosynthesis.
Grass shoots have priority over the roots for feeding. So, when cutting more than 1/3rd the remaining portion of the grass will in a sense, starve for food i.e. sugar. This ultimately creates a shallow and weaker root system.
Shallow roots and fewer available sugar mean the grass will be more susceptible to environmental stresses like heat or drought. Without a sprinkler system to water the grass often than usually this will result in the death of the grass.
Grass blades grow from the bottom, the crown, located a few centimeters above the soil surface. Removing more than 1/3rd of the length in a single mowing removes the natural cushion that protects the crown from drying out and from physical injury. The grass may turn brown and become patchy and thin if the crowns are damaged.
Even if the lawn is over grown due to excessive rain or as a result of a being away from home the 1/3rdrule still applies. Instead think of cutting the lawn multiple times, spacing the cuts a few days apart to achieve the preferred height. It may take several weeks to get back in shape, but this gradual process is far healthier for the lawn than the aggressive mowing.
When discussing newly installed sod, you must wait until the roots system have established before mowing. Depending on the season and weather conditions it may take between 2 to 4 weeks until the roots are well established for mowing.
