Sharp blades give a sharp appearance to your lawn. By the same token, dull mower blades leave your lawn looking shaggy and poorly cared for.
How can you tell if your lawnmower is clipping your grass properly? Here’s a simple test; after you have finished mowing, bend down and pluck a few blades of the grass for a close-up examination. If your mower blade is sharp, the cut edge of the grass will appear evenly sheared as if it had been cut straight across with a pair of scissors; if the cut edge is uneven and jagged, the blade is not adequately sharpened and is actually tearing off the top of the grass blades rather than cutting them.
What are the negative effects of tearing rather than cutting the grass? Appearance and health; first of all, the top edges of the torn grass will quickly turn brown as the moisture dries from the damaged part of the grass blades. This damage will weaken the grass plants and make them more susceptible to disease. Imagine what the result would be if you used a stick to knock off the tender new growth of an azalea, boxwood, or other shrub in order to prune it back, shape it, or control its growth! This is what a dull lawnmower blade does to your millions of tiny tender grass plants.
Cutting the grass with a dull blade is also a drag to the lawnmower itself—literally. The engine of the mower is under a greater strain, working harder than it should have to in order to push the dull edge of the blade through the grass. This strain can shorten the life of the engine since it is not able to operate at maximum efficiency; it also increases gas consumption.
Since we know now that a well-sharpened lawnmower blade is important to the health of the grass and to the life of the machine, how do we go about achieving the desired sharpness? With knowledge and caution, of course! First of all, put on a good thick pair of work gloves before you begin your sharpening adventure; there are lots of opportunities for scraping, mashing, cutting, and otherwise damaging your fingers in the process of removing a blade from a lawnmower, sharpening the blade, and properly securing it back onto the mower. You’ll need a short block of wood (about a foot long piece of 1”X2” pine works well), to wedge between the end of the blade and the underside wall of the cutting deck to keep the blade from free-wheeling as you loosen the bolt that holds the blade on. It is much easier to use a ratchet and the proper size socket to loosen and re-tighten the bolt than it is to use an open end, box end, or adjustable wrench. For walk-behind mowers, whether they be the 21 inch cut single blade kind or the larger deck 3 blade variety, tilt the mower deck up by pushing the handlebar down to the ground and securing the front edge of the deck off the ground with concrete blocks. The smaller mowers can be turned up on their side briefly to gain access to the blade, if you do not work too slowly, causing the gasoline to spill from the top of the gas tank.
The preferred method of sharpening is with the use of a bench-mounted emery stone electric grinder. Hold the blade securely with both hands and move it slowly along the surface of the spinning stone, being careful to maintain the original angle of the cutting edge of the blade. If you do not have a bench grinder at home, I recommend taking the blade to a professional lawnmower shop and having them sharpen the blade for you. The expense of this procedure is small and the results are well worth it in order to have a properly sharpened blade. Sharpening devices are available that can be used with your portable drill, but the results obtained are usually not very acceptable, and you certainly can not do much useful sharpening with a file or other hand tools.
Take your lawnmower blades to a pro for sharpening or take your time and do a careful professional sharpening job yourself in order to have a healthy great-looking lawn!