Proper Mowing Sharp Blade Needed For Lawns Says LSU AgCenter Horticulturist

Thomas J. Koske  |  4/19/2005 10:28:32 PM

News You Can Use For June 2004 

For a healthy, good-looking turf, you must mow properly. That’s the advice of LSU AgCenter horticulturist Dr. Tom Koske.

Mowing is what we do most to the lawn. That process removes the food-making structure known as the leaf blade; thus, we must do it properly to avoid shock.

"Simply put, we never should remove more than the top one-third of the foliage in any one cut," Koske says, or, put another way, "When grass grows out about 50 percent, it’s time to mow - even if it’s not yet Saturday morning."

By this rule, we see that lower (shorter) mowing heights will require more frequent mowing.

Mowing heights for St. Augustine are 2 ½ inches in sun and 3 inches in shade. Centipede and common Bermuda grasses are best cut to 1 ¼ inch to 1 ½ inch.

A sharp mower blade produces a prettier cut with less stress on the turf plant. Sharpening a reel mower blade assembly is difficult and best left to a professional, but sharpening a common rotary mower blade is not a big problem.

Rotary sharpening stones fit on a hand drill. They can sharpen a blade or "bring out the edge" without removing the blade from the mower housing. These, however, will just do the light-duty sharpening and will not allow for balancing the blade to reduce vibration. Plan on sharpening your blade twice a year with most grasses and three times with zoysiagrass.

The best way to sharpen a rotary mower blade is to take off the blade and sharpen on a grinder or use a metal file. When grinding, use eye or face protection and watch out for your loose clothing and sparks.

Before working on the mower, always disconnect the spark plug wire. Tilt the mower body to reach the blade and watch for leaking gas or oil. Block the blade with a chunk of wood so that it can’t move and remove the fastening bolt with a wrench or socket.

When sharpening the two cutting-end surfaces, maintain the cutting surface angle about 40 degrees. Thinner will be too knife-like and weak; it won’t hold up. Thicker angles will be more blunt and will not cut as cleanly.

As you sharpen, move the blade back and forth with light pressure. Avoid overheating the steel and losing the metal’s temper (hardness).

After sharpening, always check the blade’s balance using an inexpensive cone blade balancer or well-mounted balancer. If the blade leans more to one end, take more metal off of that end’s cutting surface to balance it.

Never try to straighten a badly bent blade or try to use a cracked blade. If the blade is damaged or the cutting surfaces worn too thin, replace the blade. Mulching blades have more bends and cutting surface than do standard high lift or bagging blades. Choose the correct blade type and length for the mower.

For related topics, look for Gardening and Get It Growing links in the Feature section of the LSU AgCenter Web site:  Additional yard and garden topics are available from an extension agent in your parish LSU AgCenter office.


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Source: Tom Koske (225) 578-2222, or

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