As lawn mower blades cut your grass, they slowly become dull over time. The blades dull more rapidly when you mow over small stones and sticks. Lawns mowed with dull lawn mower blades have ragged looking grass and carry a higher risk of contracting fungus or disease. You can either replace or sharpen dull lawn mower blades; sharpening is the less expensive option. A few tools and a little time is just enough to complete this job.
Remove the lawn mower blade from the riding lawn mower. Consult your individual operator's manual to see how to remove the blade from your particular model.
Clean the blade thoroughly with a wire brush or steel wool. Scrub it until you remove all the rust.
Place the lawn mower blade in a table vice, and clamp it down tight.
Sharpen the blade with a metal file or angle grinder. Follow the natural curve of the blade, and sharpen until the edge is nice and smooth. Ensure that you remove all pitting.
Remove the lawn mower blade from the table vice, and hold it in the center. Check for balance. If it tips one way or the other, it isn't balanced. Remove a little more material from the side that tips down and test for balance again.
Put the lawn mower blade back on the riding lawn mower.