Sometimes, trees need to be killed. When trees are in the wrong places, they can damage driveways and buildings and block sunlight from reaching a garden. Some trees are heavily invasive and choke out native growth, such as the tree-of-heaven, also known as the stinktree because of its offensive smell. Others, such as the sweet gum, drop fruits that can damage a lawn mower. Although chemicals and salt water effectively kill a tree, both methods can damage the soil around the tree, with worst-case scenarios as severe as a plot of land where nothing can grow or survive again. Copper nails do the trick but without the lasting damage.
Near the base of the target tree, hammer in a copper nail at a slight angle pointing downward. There is no standard as far as size goes when choosing copper nails, but generally, the more surface of nail in terms of both length and width, the more effective the treatment. Also, a longer nail means deeper penetration, which translates to a higher chance of the tree becoming diseased.
Continue hammering nails in a ring around the tree, about one-half inch apart. Doing so will damage an increased number of growth cells as well as increase the concentration of copper in the tree. This higher concentration is better because that will increase the chance of the metal oxidizing, which poisons the tree. The idea that one copper nail will kill a tree is only true for very small trees, such as saplings. Larger trees can tolerate a single nail without issue and will simply grow over the nail in time with no ill effects.
Cover nail heads with mud, if necessary. The purpose of covering copper nails with mud is to conceal the nails. Copper has a tendency to show quite plainly in the trunk of trees due to its bright coloring. Covering the nails makes the process less obvious with a casual glance and can preserve the look of a yard as the tree starts to die. Using mud to cover them, though, will not completely hide the fact that something has been done to the tree.
After the tree is dead, remove the nails before removing the tree. Otherwise, the nails could fly out and injure someone or they could damage the machinery being used to remove the tree since there are many nails.