Instead of a clean "scissor cut," a rotary-mower "whacks" the grass blade off. Therefore, it is especially important to keep rotary mower blades very sharp. Remember to balance the blade if you sharpen it yourself.
"Mow grass in the coolest part of the day for the cleanest cut." Grass blades are more turgid when they aren't under heat stress (Example: hot summer afternoons). However, dew interferes with good early-morning mowing, especially if you are mulching your clippings, so evenings are usually best for lawnmowing. Also remember that "wet grass conditions" will aid in the spread of turfgrass disease pathogens that are already present on your lawn.
This saying reminds us to cut turfgrass at the highest setting possible. 2-1/2 to 3 inches is the ideal mowing height for most home lawns. Grass growing in the shade needs to be cut as long as possible, since it needs more leaf area to intercept limited sunlight.
Example: If your lawnmower is set at 3 inches, always cut it before it gets beyond 4-1/2 inches in height.
Mulching your grass clippings helps return nutrients and organic matter to the soil. Try to mow often enough, under dry enough conditions, so that clumps of grass aren't left on the lawn. If you have a thick thatch layer on your lawn it is advisable to bag your clippings for composting. Clean your mower deck after mowing.
LATE FALL LAWN MAINTENANCE
(This would be November in the northeastern US)
Ensure your grass is cut short enough (but not scalped) to prevent it from "laying over" under deep snow cover. Using a 2 to 2-1/2 inch cutting height should be sufficient. It's actually best to gradually lower your cutting height over the final three cuts of the year, instead of trying to shorten it all in one final cut. Shorter grass is less likely to suffer from snow mold disease. Check for any last minute leaf accumulations that may smother grass.
Bleached-out, dead-looking grass is a typical symptom in Spring. These fungal lawn diseases occur during winter and are most severe where snow cover lasts much of the winter. Gray snow mold is the least serious killing only grass blades, while pink snow mold can kill crowns and roots.
If your lawn soil test calls for lime, late Fall is considered the best time of year to make a lime application. Retest your lawn soil every three to five years for deficiencies. Aerating your lawn in conjunction with a lime application helps get lime into the root zone faster!
Late Fall is the time to apply "winterizer" fertilizers -- these are usually high in potassium, which improves winter hardiness and disease prevention. Even though top growth of your lawn has ceased, the roots remain active to "pick up" the nutrients. If you're applying both lime and fertilizer, it's best to separate the applications by two weeks.
After the final cut, service your lawnmower: Add fuel stabilizer to the gas tank and run the engine for 5 minutes to stabilize the complete fuel system. Perform all other scheduled lawnmower maintenance such as an oil change and lube, cleaning the air filter, replacing worn out or damaged parts and sharpening the blade(s). This would also a good time to install a new spark plug, after setting the correct gap.