Most cool-season grasses should be cut when they reach heights of 3 to 3 1/2 inches, typically once a week.
Cut warm-season grasses when they reach 2 to 2 1/2 inches. Cut no more than one-third of the grass height at each mowing to avoid damaging the plants. If the lawn grows too high for you to cut off one-third the height and have an acceptable length, cut off one-third now and one-third again in two or three days.
Cutting more than one-third the height results in clumps of clippings that tend to lie on top of the lawn, decompose more slowly, and give the grass a less attractive, open, bristly appearance. In addition, short cutting will stunt or slow root grow and weaken the plants. But these aren’t the only reasons not to cut your grass too short:
First, grass grows from the crown, not the blade tips. This trait makes grass ideal for lawns because it keeps on growing despite the regular mowing off of its upper stem, leaf sheath, and blades. This is also why it’s important not to damage grass crowns by accidental scalping with the mower.
Second, keeping grass on the longer side allows it greater surface area to carry out photosynthesis. This in turn results in healthier plants.
Third, taller grass grows slower than shorter grass. You can use this simple fact to eliminate up to 20 percent of the mowing you do annually. That’s a saving of about eight hours a year for the average lawn owner, not to mention the savings on gasoline and wear on the mower.
Lastly, by keeping your grass at the upper end of its recommended mowing height, you can prevent most weeds from germinating and thereby eliminate the need for herbicides. Following are some additional general lawn-mowing tips:
1. Mow only when the grass is dry.
2. Change mowing patterns frequently to prevent compaction.
3. Leave clippings on the lawn unless they are very long or wet.
4. Mow with a sharp blade. Resharpen after every 10 hours of use. Bring the blade to a professional sharpening service once a year. Replace the blade as necessary.
5. Rinse the grass clippings off your mower after it has cooled to reduce the chance of spreading lawn disease.
6. When it is hot, cut grass at the high end of the recommended height range; cut at the low end of the recommended height range during cool weather or in shade.
7. Make your last cut of the season at the low end of the recommended height range.