After a tree or bush is cut down, the root system is still alive. It may die naturally due to shock, but in some cases, the decay process needs a helping hand. Using natural ways to kill stumps is safer for the rest of your garden than using herbicides.
Cut the stump as close to the ground as possible. Using an ax or saw, score the top and side with cuts to speed up the natural decay process.
Cover the stump with a can. This method works best with smaller tree stumps or bushes. The metal will cut off light and oxygen. Pound the can into the surrounding soil a few inches to anchor it.
Use boiling water. Liberal doses of boiling water can kill just about anything by cooking it. The key is to get the boiling water into the root system to burn the roots and prevent new growth.
Use plastic sheeting for bigger stumps. Much like using cans for smaller stumps, covering a stump with plastic sheeting smothers the stump and prevents sunlight from reaching it. After covering the stump with plastic, add mulch or dirt on top to hold the sheeting in place and camouflage the plastic.
Speed up decay with salt. Drill holes in the stump on top and along the sides. Fill the holes with rock salt as a natural root killer. For smaller stumps, the salt may be poured directly over the wood in small mounds.