It's important to keep your pruning tools, including clippers and shears, sharp, not only to ensure they work as they should, but to protect your plants. Dull clippers rip through stems as they trim, creating a wound that takes longer to heal than one that's sharply cut. Dull, dirty tools may also spread weed seeds and plant disease. Moreover, sharp tools are simply easier to use. It's best to sharpen clippers with a stone or a file; a power tool, such as a rotary tool, is more difficult to control and may ruin the edges. Wear protective gloves -- the blades are sharper than they appear.
Disassemble the Tool
Whether you're sharpening hedge trimmers, bypass clippers or anvil loppers, the job is easier if you can disassemble the tool, but do this only if the tool is not spring-loaded. Unscrew the nut that joins the blades, using a wrench. Remove the nut, bolt and washer, and put them in a safe place.
Clean Off Rust and Sap
Wipe off sap and resins with a rag soaked with alcohol, mineral oil or spray lubricant.
Remove rust by sanding or scrubbing with a wire brush or a steel wool pad, being careful to keep your fingers away from the edge of the blade. If the blades are seriously rusted, dissolve the rust by spraying vinegar on the blades and leaving the tool for several minutes. Lemon juice, baking soda and cola also dissolve rust.
Clamp the Tool
Clamp each blade in a vise; if you didn't disassemble the clippers, clamp the entire tool so that one of the blades is facing up. Place the file or stone flush against the bevel of the blade -- look carefully to ensure you gauge this correctly, because if the sharpening tool is at an angle to the blade bevel, it won't hone the edge properly.
Sharpen the Blade
Draw the file or stone along the edge, moving it away from you on each stroke. Stop after about five strokes and feel the edge carefully with your ungloved finger. Stroke a few more times if it doesn't feel sharp enough. Turn the blade or tool over and sharpen the other edge if there is a bevel on that side. Bypass clipper blades usually have a bevel on only one side, but anvil clippers have bevels on both sides.
De-burr the Edge
Run the file or stone lightly along the edge of the blade to de-burr it after you've sharpened it.
Clean and Oil the Metal
Wipe the blade with a rag soaked with alcohol after you've sharpened it, to remove fine metal shards and to disinfect it. Put a few drops of mineral oil on the blade and rub it in with another rag.
Lubricate the Clippers
Reassemble the clippers, if you took them apart, and tighten the nut enough to make the blades cut smoothly but remain loose enough to make the tool easy to use. Whether or not you took the tool apart, lubricate the joint with a few drops of penetrating oil.