Many gardening tools, particularly shovels and hoes, are both easier to use and more effective when the edges are sharpened. Sharp tools not only move through the soil with less force, but cut roots much more easily.
Any time you are using a shovel for transplanting or even for root pruning in preparation for transplanting, you will find the work much easier if the shovel used has a keen edge. Unlike knives or woodworking tools, garden tools need only a well-formed edge, not a honed edge. A shovel or a hoe can easily be sharpened in a few minutes with the right tool.
The right tool is a mill file, single cut on one side and double cut on the other. The double-cut side is used for fast stock removal and the single-cut side is used to smooth the final edge.
This file is 11-1/2" long overall with 7" of cutting surface and has an integral handle with a hole in it so that it can be hung in an easily visible spot in a garden shed.