Copper sulfate is known for its root-killing properties, but the chemical will also destroy bacteria and fungi. While copper sulfate has many benefits to gardeners and homeowners because of its lethal nature, remember that the chemical knows no distinctions. When applied in large quantities or improperly, copper sulfate may kill all roots and bacteria, even those that are beneficial or desirable.
Copper sulfate will kill roots when it comes into contact with them, and works so well that effects may be noticed within a single day. But copper sulfate's power is very much localized, and not likely to spread to surrounding plant systems and soil. In the main, copper sulfate is applied to tree roots that are spreading into underground systems, commonly plumbing. It not considered an effective defense against weeds, which grow close to other, more desirable plants. Remember that, though the effects of copper sulfate are localized, the chemical is not selective.
Copper sulfate is used to rid sewer lines of tree roots, which cause stoppage and damage to plumbing. To use the chemical as an effective treatment against roots in the sewer system, pour the crystals into the toiler. Apply copper sulfate only in small amounts, 1/2 cup per application. Flush the toilet repeatedly, up to 12 times, after each application to move the crystals down the line and toward the troublesome roots. Do not pour the crystals into lighter plumbing lines, such as sink and tub drains, as it may damage metal pipes.
It may take weeks for copper sulfate to effectively kill all troublesome roots in a sewer system. In some cases, however, copper sulfate may work very quickly to dissolve damaging roots. Begin flushing 1/2 cup of copper sulfate down the toilet when a root blockage is present in the sewer line. Wait one month before the next application if results are incomplete or unsatisfactory. Copper sulfate may also be used preventively when small amounts are placed into the sewer. Add 1/8 cup of copper sulfate to the system every three or four months to dissolve roots before they grow large enough to create problems.
Copper sulfate may also be added to septic tanks, both to kill bacteria and tree roots, but it is not recommended that it be introduced into the system through the toilet. Add 2 pounds of copper sulfate to a 300-gallon septic tank twice a year, using the distribution box if one is available.