Tree killers work by killing the roots of the tree through dehydration or over-saturation or by blocking photosynthesis. Some methods that incorporate simple ingredients include salting the tree to dehydrate the root system, feeding large amounts of vinegar to the tree to inhibit the photosynthesis process, covering the tree to block sunlight and over-mulching the ground around the tree to over=saturate the roots.
When using salt as a tree killer, it is recommended that rock salt be applied directly to the tree stump via holes drilled into the wood. This is to prevent the ground around the tree from becoming hostile to other plants. After the salt is poured down the holes, the stump should be covered with sheet plastic, or the holes should be taped over. It takes a few weeks for the root system to die.
Vinegar is applied to the tree stump in the same way that rock salt is applied. The vinegar is continuously added to the holes over about a month before it dies. The vinegar slowly kills the living tissue of the tree and keeps the tree from transferring carbohydrates to the roots by blocking photosynthesis. Blocking a tree from sunlight does the same thing, but it takes a lot longer to work and is not a good option for large trees.
To kill a tree with mulch, a thick 8-to-10-inch layer of mulch is applied to the base of the tree. This makes the tree appealing to creatures who feed on moist wood by causing the tree to retain too much moisture. The roots become shallow, and the tree becomes unstable. This method takes several months to a year to work properly.