Although you need to take reel mowers to a lawn mower shop for a professional sharpening, you can sharpen rotary mower blades yourself. Of course, you need to check the owner’s manual for specifics, but basically, the procedure is as follows:
Turn the mower off and disconnect the spark plug.
How often your blades need to be sharpened depends on how large your lawn is, the type of grass you have, and a bunch of other things. If you have a small, cool-season lawn you may need to sharpen the blade only once a year. More wiry grasses, such as Bermuda grass, may dull blades faster. But don’t worry, your lawn shows you when its time to sharpen the blade.
Remove the blade with a wrench.
Wear heavy duty work gloves any time you work with lawn mower blades.
Secure the blade in a vise.
Maintain the existing angle on the blade and sharpen with a smooth, easy pass with the file.
Check the balance of the blade by centering the blade (not the sharp side!) on top of your finger or a dowel.
Dull blades leave a ragged edge on the top of the grass blade, giving the whole lawn a browned-out look a day after mowing.
Reinstall the blade, making sure that it’s right side up. Secure locking nut.
If the blade doesn’t balance, file a little more off the heavy end until it does. Or, forget the whole thing and buy a brand new blade. You can usually get one for less than $10.
You should sharpen your mower blades before your lawn shows any damage, and few blades should go a full season of mowing without sharpening, even on small lawns. Also, you need to periodically examine mower blades for damage that may occur, such as nicks from hitting a rock or sprinkler.