Trees and Shrubs Bad; Grass Good
Trees and shrubs should be planted at least 10 feet away from the edges of any septic system (tank and fields).
If trees or shrubs are planted too close to the septic area, the roots of these plants seek the water inside the septic system. As the roots grow into the gravel and septic pipes, they push dirt into the system. Over time the roots push more and more dirt into the system, until finally the gravel and pipes are filled with dirt and roots, making the system ineffective. The picture featured above shows a pipe that is completely filled with roots and dirt.
There should be no vegetation, except grass, growing over or around your septic system. Grass assists the septic fields as some of the water surfaces for evaporation and transpiration. Keeping the grass over a septic system properly mowed promotes the evaporation and transpiration process.
However, if the fields are beginning to fail, water will surface in puddles, making the ground swampy. Thick grass patches or soft ground are also indicative of a failing system.