Cleaning your garden tools regularly after use is ideal, but at the least they should be cleaned before putting them away for winter. Clean tools work more effectively, so are easier to use, and they last longer.
Keeping blades sharp improves cutting, which is easier on you and the plants. Keeping tools used in soil cleaned keeps their edges sharper too, preventing rust from forming, and removes possible disease-laden soil particles. Cleaning tools even more often when working on infected plants is essential to prevent disease spread. If pruning diseased limbs from trees, keep a container of rubbing alcohol, bleach (one part to 9 parts water), or disinfectant (such as Lysol) handy to dip blades in between pruning each plant to avoid spreading disease.
For tools such as shovels, hoes and garden forks that are used in soil, wash them after use with a forceful stream of water from the hose. For stubborn soils such as clay, use a wire-bristle brush or dull implement if needed. Then dry tools with a rag. For blades of saws and pruners that end up with sticky plant sap, such as from evergreens (pines, spruces and the like), use some paint thinner to remove the sap before wiping with a rag.
Even after cleaning, the worn metal can rust, even more so if higher grade steel. To prevent this, wipe tools or spray with a very light coat of motor oil. Some dilute this with kerosene, 2 parts oil to one of kerosene. Others recycle their old oil from mowers for this use. You can wipe the oil on with an old rag or paper towel, spray it on with a hand sprayer, or make a mix of the soil with sand to push tools into after each use. The latter is easy, quick, and the sand helps provide some abrasion to remove soil in the process. The oil breaks down rapidly in the soil, and little is used, so you shouldn’t have any negative soil effects.
For hand tools, some use a strong black tea. Brew up enough in a pan or kettle to cover the tools, then let them, or blades at least, soak for a few hours after the tea is cooled. Rust should wipe off easily with a rag. If tools aren’t very dirty or rusty, a balled up handful of wax paper rubbed over surfaces may be sufficient—both cleaning and leaving some protective wax on them.
If tools have gotten severely rusted, you may need to use rough sandpaper, and even perhaps a wire bristle brush. For the most rusted, you may need to use a drill with wire brush attachment. For the latter in particular, make sure to wear safety glasses. Then make sure to wipe and coat with oil.
Sharpen tools too, at least at the end of the season. Best is to sharpen them regularly as used during the season. This is more important if tools have rusted. For dull large tools such as shovels, axes, and spades, you can use a hand file available from hardware or home stores. If very dull, you may need a high speed grinding stone or drill attachment. As with cleaning, make sure to wear eye protection if using a high-speed grinder.
If using a grinder made for this purpose, as some do with lawn mower blades, it is easy to get carried away. If the metal heats up too much it can lose its “temper”, meaning it won’t hold an edge well again. If grinding, keep the metal from heating by dipping in cold water. It should remain cool to the touch. Improper sharpening of mower blades can make them out of balance, which can harm the mower motor as it turns at high speeds.
For finer tools such as pruners and loppers, an oil stone or honing stone is what many gardeners use. I spend a bit more for a good quality handfile, such as with cut diamond or carbon surface, to make the job go much better and more quickly.
Whatever sharpener you use, follow any directions so they work properly. If using a stone, slide the blade along the stone in one direction, doing so repeatedly until sharper. If using a file, such as “mill file” from a hardware store, get one with a handle so you can maneuver it more easily. Draw the cutting teeth of the blade along the edge of the tool in one direction. Keep the file at an angle to the edge of the tool surface you’re sharpening.
So how sharp is enough? Anything of course helps. Tools such as shovels and hoes don’t need to be as sharp, and pruners should be more sharp. You can feel the sharpness with fingers (be careful if sharp knives or pruners), or just look at the “bevel” and angle. The bevel is the sharpened edge, the angle is between the two edges or bevels. Duller tools have a shorter edge or bevel, and generally wider angle—perhaps 30 degrees between the sides or bevels. Sharper tools have a longer bevel, and more narrow angle between each side—perhaps 15 degrees or so.
Many tools now have plastic handles, but if you have one with wood, treat it as well for longest life. Rub wooden handles with a rag, slightly moistened with linseed oil or other wood protection oil product.
Once tools are cleaned and sharpened, store them properly in a closet, garage, or shed out of the weather. Keeping them off the floor helps prevent any moisture and rust, and dulling. I like to hang mine by the handles. If straight handles, I hang upside down with ten-penny nails used to hold the tool itself. When buying new tools consider stainless steel ones, if available, that are easier to keep clean.