Pruning shears are fundamental tools for any gardener, providing the clean cuts necessary for healthy plant growth. Over time, the constant use of these tools against woody stems dulls the cutting edge, making pruning difficult and potentially damaging to the plants. Using a sharpening stone, also known as a whetstone, is the most effective way to restore the blade’s precise geometry. This process requires careful preparation and technique to ensure the shears perform like new.
Preparing the Shears for Sharpening
Before sharpening, the shears must be completely cleaned to remove debris that would clog the stone. Wear heavy-duty gloves and eye protection before handling the blades. Plant sap, dirt, and rust must be scrubbed away, as they interfere with sharpening and could damage the stone’s abrasive surface.
For a thorough cleaning, disassemble the shears by removing the central pivot bolt, especially with bypass types. Sap and resin can be dissolved using an oil-based lubricant or specialized cleaning product. Rust can be treated by soaking the blades in white vinegar for a few hours, followed by scrubbing with a wire brush or fine-grade steel wool. The blades must be completely dried after cleaning to prevent immediate flash rusting before proceeding to the sharpening stage.
Selecting the Stone and Identifying the Angle
Choosing the correct sharpening stone involves selecting appropriate grit levels. Dual-sided stones are common, featuring a coarse side (100–300 grit) for repairing nicks or reshaping damaged edges. The finer side (600–1,000 grit) is used for honing the blade and achieving a smooth finish. Stones require a lubricant (oil or water) to float away metal particles and prevent glazing; commit to one type and never mix them.
Identify the existing bevel angle of the cutting blade before touching the stone. This angle, typically 20 to 25 degrees for bypass shears, is the slope that tapers down to the cutting edge. Maintaining this factory angle is important, as altering it results in either a weak edge prone to chipping or a blunt edge that crushes plant material. To confirm the angle, observe the existing bevel or use a marker to color the edge; the correct angle is found when the stone removes the ink evenly across the bevel on the first few strokes.
The Sharpening Technique
Prepare the stone by soaking it in water or applying a thin layer of honing oil. Push the blade edge into the stone, moving from the heel (closest to the pivot) to the tip in a steady, consistent stroke. Maintain the identified bevel angle throughout the motion, using the stone to abrade the metal and restore the edge.
Bypass shears have a bevel only on the outside edge of the cutting blade, and only this side should be sharpened. Anvil shears also have a single-sided bevel that requires sharpening. The flat, un-beveled side of both shear types must not be sharpened, as it must remain flat to function correctly.
After several passes with the coarse grit, a small curl of metal, known as a burr, will form along the flat side of the blade. This burr indicates the metal has been fully worked and the new edge is established. Switch to the fine side of the stone and repeat the angled strokes on the beveled side to refine the edge and reduce the burr. Finally, lay the flat side completely flat against the fine stone, making one or two light passes to completely remove the burr.
Finishing and Testing the Edge
After sharpening, clean the blades again to remove abrasive particles or metal filings that could cause friction or rust. Wipe down the blade surfaces with a rag and a few drops of oil, ensuring no grit remains. If disassembled, reassemble the shears, paying attention to the correct alignment of the cutting blade and the counter blade.
Apply a drop of lubricating oil to the pivot point and coat the entire blade surface to protect the steel from corrosion. High-quality tool oils or light machine oil keep moving parts operating smoothly and prevent rust. To test sharpness, hold a piece of paper taut and cut it with the shears; a sharp edge will slice through the paper cleanly without tearing. Alternatively, sever a small, soft branch with minimal effort, resulting in a smooth, uncrushed cut surface.