Using salt is an effective way to kill a tree. The sodium in salt will prevent a tree's flow of potassium and magnesium, both of which are vital ingredients in the making of chlorophyll. The lack of chlorophyll will eventually kill the tree. You can simply make a line of salt around the tree, and it will die. However, most everything around the tree will die as well. Because of this, you need to take measures to concentrate the salt around the tree to ensure you minimize the destruction around the tree.
Drill four to six 1/2-inch holes around the tree. Position the holes diagonally in the tree. Start drilling approximately five inches up from the base of the tree, and angle the drill bit in a downward position. Drill at least 3 inches deep.
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Pour 3 cups of water into a container, then add 6 cups of salt. Mix the two together. You can change the amount of solution you mix by maintaining a ratio of one part water to two parts salt.
Pour the solution into the holes you drilled into the tree. Monitor the solution. When it dissipates, refill the holes with more. Continue doing this weekly until the foliage on the tree turns brown and dies.