There are many things to remember regarding watering, fertilizing, and mowing your lawn, but the one-third mowing rule is one of the most critical aspects. This rule minimizes stress and helps keep your grass healthy by only removing one-third of the grass blade as you mow.
Understanding the one-third mowing rule
The one-third mowing rule — which advises never cutting more than one-third of the grass blade height at a time — is a widely recommended lawn care tip to keep grass healthy and vigorous. It helps reduce stress on your lawn and recover more quickly after mowing. Cutting off only a third removes enough to keep your lawn looking good without stunting growth.
| To remove one-third of the blade length | ||
| Grass type | Recommended cutting height | Mow when turf reaches |
| Kentucky bluegrass | 2.5-3.5 inches | 3.75-5.25 inches |
| Turf-type tall fescue | 2-3 inches | 3-4.5 inches |
| Perennial ryegrass | 1.5-2.5 inches | 2.25-3.75 inches |
| Creeping red fescue | 3-3.5 inches | 4.5-5.25 inches |
| St. Augustine | 2-3 inches | 3-4.5 inches |
| Zoysia | 1-2 inches | 1.5-3 inches |
| Common Bermudagrass | 1-2 inches | 1.5-3 inches |
| Hybrid Bermudagrass | 1-1.5 inches | 1.5-2.25 inches |
| Bahiagrass | 3-4 inches | 4.5-6 inches |
| Centipedegrass | 1-2 inches | 1.5-3 inches |
How did the one-third mowing rule come to exist?
While the origins of the one-third rule of mowing are debated, they are rooted in agronomic and horticultural research focused on turfgrass management best practices.
Iowa State University Extension and Outreach has this to say about the rule’s origins:
“The one-third rule originated from a greenhouse study done by U.S. Department of Agriculture scientists about 60 years ago on forage-type Kentucky bluegrass. The goal of the study was to investigate the effect of cattle defoliation on the growth of the roots. Results of the study showed the grass (or roots) didn’t die when more than one-third was removed. The growth of the roots simply paused for a short time before resuming normal growth. The findings from this study were eventually morphed into the creation of the one-third rule.”
Negative effects of cutting more than one-third
Mowing more than one-third of the grass’s height can cause several negative consequences that affect the health and appearance of your lawn. Here are some of the most significant impacts:
- Prohibits photosynthesis and energy production: Grass blades are essential for photosynthesis, absorbing sunlight and carbon dioxide to make energy for the plant. Cutting too much of the grass blade off at one time reduces the grass’s ability to produce energy, weakening it and making it more susceptible to environmental stresses like heat and drought.
- Reduces root growth and development: Severe mowing can reduce root growth, as the plant allocates resources to regrow the lost blade tissue instead of sending energy to the roots. When you follow the one-third rule, the plant is better at maintaining a healthy balance between above-ground and below-ground growth.
- Makes it harder to handle stress: Cutting more than one-third of the grass blade at a time can cause significant stress, which leads to browning and increased vulnerability to weeds, pests, and diseases. The one-third rule helps minimize stress, promoting a healthier and more resilient lawn.
- Increases weed pressure: Mowing too short prevents the blades from intertwining and shading the soil surface, which can exacerbate common lawn weeds. When the soil isn’t shaded, grassy and broadleaf weed seeds get more sun, increasing their chance of germinating and taking off.
- Increases thatch accumulation: When you remove more than one-third of the blade, the grass clippings take longer to break down and may lead to quicker thatch accumulation. Excessive thatch can prevent water, air, and nutrients from reaching the soil and roots.
FAQs about the one-third rule of mowing?
How do you mow grass that has gotten too tall?
In instances where you haven’t been able to mow, and the grass grew too tall (vacations, prolonged rainy stretches, mower mechanical problems), the best thing to do is gradually bring the height back down to the recommended height. Raise the height on your mower deck, and mow more frequently, dropping the deck each time until your grass reaches the desired height. As always, try to never remove more than one-third of the grass height at a time.
How long should I wait between mowing the lawn?
It’s optimal to mow your lawn every seven to 10 days. Each mow stresses the grass, so you want to spread out mowing events as long as possible.
However, this time frame may be shortened when your grass grows like crazy: spring and fall for cool-season grasses and summer for warm-season grasses. When it’s growing so rapidly, instead of cutting every three or four days, it may be best to let your lawn stay a little taller, which enables you to go a little longer between cuttings.
Does frequent mowing make grass thick?
Frequent mowing alone won’t make your grass thick. Instead, a combination of best practices promotes grass health and keeps it dense: follow good watering practices, mow at the correct height, avoid removing more than one-third each time, keep mower blades sharp, fertilize according to your grass type, and control weeds. All of these together will create a vigorous, thick lawn.
Let the professionals worry about mowing height
We get it — sometimes schedules get busy, you head out of town on vacation, or a cool, rainy season thwarts your attempts to keep your lawn on track. There’s no need to stress over when you can get outside and get that jungle under control. That’s why we’re here!
Reach out to Lawn Love, and we’ll connect you with local lawn care professionals dedicated to keeping your lawn at the proper mowing height so it flourishes and looks beautiful. You can sit back and let them worry about how much they should or shouldn’t be taking off at any given time.
Main Image Credit: irontrybex | Adobe Stock | License
