Garden News: Sharpen those mower blades

A healthy, good-looking lawn requires proper mowing. Because it removes the food-making structure known as the leaf blade, we must do it properly to avoid excessive stress to the plant. And that means a sharp blade, says LSU AgCenter turf expert Ron Strahan.

Simply put, never remove more than the top third of the grass in any one cut, Strahan says. When the grass grows back about 50 percent, then it’s time to mow again — even if it’s not Saturday morning.

The proper mowing height for St. Augustine grass is 3 inches. St. Augustine grass becomes more disease-prone and overrun with weeds when it’s cut shorter.

Centipede grass and common Bermuda grass perform best when maintained at 1½ inches. Hybrid Bermuda grasses need to be maintained at about an inch.

A sharp mower blade produces a prettier cut with less stress on the plant. Maintaining a sharp mower blade on a push mower is not that difficult. Sharpening stones that fit on a hand drill can sharpen a blade or bring out the edge without removing the blade from the mower housing. These, however, will just do light-duty sharpening and won’t allow for balancing the blade to reduce vibration.

The best way to sharpen a rotary mower blade is to remove it and sharpen it with a grinder or metal file.

Before working on the mower, disconnect the spark plug wire and tilt the mower body to reach the blade watching out for leaking gas and oil. Wedge the blade with a piece of wood so it can’t spin, and remove the blade’s fastening bolt with a wrench. Note the top and bottom of the blade and replace it in the same position.

Sharpen the cutting surfaces at about 40-degree angles. Thinner will be too knife-like and weak. Thicker angles will be blunter and not cut as cleanly.

After sharpening, always check the blade’s balance using an inexpensive, cone blade balancer or even a nail pivot in a wall or stud. If one end of the blade is heavier than the other, remove more metal from that end’s cutting surface to balance it. A balanced blade will vibrate less and cause less engine wear.

Got a gardening question? Write to GardenNews@agcenter.lsu.edu.