As long as you use nails that are big enough to enter the growth cells under the bark, you can kill trees with copper nails. Disease and infection caused by the nails will eventually kill the tree. Although it may take a bit of time for the trees to die, killing trees with copper nails is a simple process that only requires the nails and a hammer.
Mark the nailing locations around the bottom of the trees near the root system. Use the claw of a hammer to make small notches in the bark. Make three to five notches on each tree.
Hammer copper nails that are at least 2 inches long into the trees that you want to kill. Place the pointed end of a copper nail against the notched bark and hammer it all the way in. Hammer copper nails into all of the notches.
Add more copper nails to the tree's trunk, if necessary. If you don't see signs that the tree is dying within about four months, hammer additional nails into the tree's base.