How to Sharpen Hedge Shears
Before sharpening hedge shears, check the pivot nut. The nut should be snug with no play. If the shears still cut poorly, look down each blade to make sure it's not bent. If a blade is slightly bent, loosen the pivot nut and separate the blades. To straighten the blade, put it in a vise, slip on some thick leather gloves and tweak it until it's straight.
Next, file the edge to expose clean metal. Examine the factory edge. Hold the file with both hands and mimic the direction of the bevel. Now move the file in one broad stroke away from you along the entire cutting angle. Don't use small, jerky strokes or you'll lose the factory edge. As you work, you can see the clean metal path left by the file. Adjust your angle as needed to file the entire edge evenly. Repeat this motion several times until you expose clean metal over the whole edge. Usually it'll take only about 10 strokes. Do the same with the other blade.
Finally, sand the back side of the blade. Place a sheet of 300-grit wet/dry sandpaper on a smooth, flat piece of plywood. You'll be able to feel the burrs (be careful—they're sharp) on the back side of each blade. To remove them, lightly sand the back side of the blade. Keep the blade flat and move it in a circular motion. After making several circles, pick up the blade and gently feel the edge. When the burrs are gone, assemble the blades and lightly oil the moving parts with 3-In-One oil.