Many gardeners don't even think about sharpening shovels, but the blades can become dull after several seasons of use. Sharpening a shovel takes just a few minutes and you'll notice a huge difference the next time you use it. A sharp shovel cuts through soil, sod and stubborn roots far more easily than a dull one, which means you'll save both time and effort.
Remove dirt from the shovel blade by gently scrubbing the metal surface with a wire brush or steel wool. Use naval jelly or penetrating oil and an emery cloth to get rid of rust, if necessary.
Attach the shovel securely onto a work bench with a C-clamp or a bench vise. Position the shovel with the head near the clamp and the concave side facing up.
Determine which side of the shovel has the leading edge by lightly running your finger along the underside and then the top of the blade. You only want to sharpen the leading edge, or the side that feels sharper to the touch.
Use a 10-inch flat mill file to sharpen the leading edge of your shovel. Using moderate pressure, push the file away from you and down in long strokes. Maintain a consistent angle along the full length of the blade. You want to form a slope, which is called a bevel, of about 70 degrees to the shovel's upper surface.
Take the occasional break from filing, and run your finger along the underside of the blade. You're finished sharpening the leading edge once you feel a burr, or a slight ridge, along the entire length of the shovel blade.
Apply a thin coating of lightweight honing oil over the entire blade. Wipe off the oil if you plan on using the shovel right away, but leave it on and allow it to penetrate the metal if you're going to store the tool for a while. The oil helps prevent rust from forming on the blade.