Potassium nitrate (KNO3), sometimes called saltpetre or nitre, is a key ingredient in many chemical stump removal products. When applied properly, potassium nitrate greatly accelerates the natural decomposition process of a stump, often making the wood weak and rotten enough to break up and dispose of easily within a matter of weeks. Historically, potassium nitrate has been used as an ingredient in gunpowder, but it also a common fertiliser and has been used as a food preservative, so stump removers containing it should be safe and effective when used according to directions.
Trim stump. If the stump is not already cut off very close to the ground, trim it as low as possible. This will allow your potassium nitrate to work more quickly and effectively by reducing the amount of wood to rot.
Drill top holes. Use a 1-inch drill bit to bore several holes into the top of the stump. As possible, make the holes roughly 12 inches deep, and locate them several inches from the outside edge of the stump.
Drill side holes. Bore several holes into the side of the stump. Drill downward at a 45-degree angle, and try to drill into the vertical holes from step 2. This will allow air, water and potassium nitrate to penetrate more of the stump and speed its decaying action.
Add potassium nitrate. Pour 3 or 4 oz of potassium nitrate into each of the vertical holes, and then fill the holes with water.
Wait several weeks. The potassium nitrate will speed up the natural decomposition process, causing the wood to soften and rot. After a month or six weeks, the decay should be advanced enough to proceed.
Remove stump. Break apart the stump using a spade, mattock, axe or similar tool. You can then dispose of the pieces as desired and fill and cover the hole where the stump was.
If you buy stump remover, carefully follow the manufacturer's instructions. They will likely be very similar to the steps listed, but products can vary, so it is always best to adhere to the guidelines for your specific product. To help hasten decomposition, cover low stumps with dirt or sod and try to keep them damp.
While burning out a rotted stump with kerosene or fuel oil can be effective, it is also dangerous, because the stump may smoulder slowly for several days. This approach is not recommended, even if you take precautions to manage and monitor the blaze.