Concave cutter

A concave cutter is a specialized bonsai pruning tool with curved, cupped blades designed to remove a branch flush to the trunk while leaving a shallow, bowl-shaped wound rather than a flat or raised stub. That hollow shape matters because bonsai bark heals from the edges of a wound inward, so a concave cut closes into a smooth, barely visible scar instead of a raised bump.

Using a concave cutter well means cutting close enough to the trunk that no stub remains, since stubs do not heal over cleanly and can die back or invite rot. On thicker branches, growers often make an initial rough cut with a saw or knob cutter, then finish and hollow the scar with the concave cutter for a cleaner result than the concave cutter could achieve alone on a large branch.

A common mistake is using ordinary shears or a knife for these cuts, which leaves a flat or convex scar that heals into a visible ring or callus. Sealing larger wounds with cut paste after using a concave cutter also speeds healing and reduces the chance of dieback around the cut, especially on species prone to slow callusing.