When you landscape over a septic system drain field, most landscapers recommend shallow-rooted plants such as annual flowers or drought tolerant grasses. Trees with deep roots can grow down into gravel surrounding pipes and might invade cracks in the pipes, widen and break them. Water-loving trees, such as willows, even planted at a distance will send roots in the direction of the pipes and cause problems. If you have problem tree roots in your septic system, you can temporarily rescue your pipes by flushing them with salts from a water softener to dissolve the root hairs of invading roots.
Select salt that is used in a water softener to kill tree roots. Common salts used in water softeners include rock salt, solar salt or evaporated salt. Rock salt is available commercially from any grocery store.
Measure 1 cup of rock salt using a measuring cup.
Pour the salt into the toilet and flush.
Measure and flush rock salt again every two weeks.