By:
Tim Daly

One of a homeowner’s worst nightmares is damage to their septic tank system causing wastewater to seep out into their yard and sewage to back-up in their homes. Many factors can lead to septic system problems, but one of the most common causes are the roots of trees and shrubs seeking out the septic system for water and nutrients.

They can penetrate the pipes causing them to become clogged. The Extension office frequently receives calls from homeowners inquiring into the type of plant material to choose with roots that will not interfere with the functioning of their septic systems. Some plants are more likely to cause harm than others.

First, you need to understand some basics of a septic tank system. A septic tank receives wastewater from a house. It then filters out solid material and distributes the water into other areas of your yard, called a ‘leach field’ through underground perforated pipes surrounded by gravel. The wastewater slowly soaks into the soil. Microbial organisms break down the material filtering and cleansing it before reaching groundwater, thus minimizing pollution. If the system is functioning correctly, the process is sanitary and efficient.

Grass and herbaceous plants, such as annual and perennial flowers, as well as ornamental grasses, can be safely planted over septic drain fields since they have shallow roots and will not grow into the pipes. Trees and shrubs are a more significant challenge since their roots penetrate deeper into the soil. Once they find the moisture and nutrient source of the septic drain field, they can invade the pipes and impede the flow of wastewater.

Know the location of the septic tank and its accompanying drain field, and install trees and shrubs away from these areas. Some plant material with shallow growing, less aggressive root systems can be planted closer the drain fields, but not directly over it. Shrubs such as hollies, azaleas, and Indian hawthorns, and certain trees, such as dogwoods or redbuds, can be planted in the vicinity of the drain field. Their roots have a lower probability of invading the pipes. Certain trees should be avoided entirely, such as weeping willows, red maples, silver maples, river birches and other trees with more aggressive growing roots.

How do you determine the distance the root system will extend outward from a tree? The roots spread out two to four times the diameter of the canopy. Also, they continue outward three times the height of the tree. These distances are a rough estimate, and the trees and shrubs should be spaced even further out to be on the safe side.

Often the question about the safety of growing vegetables over a drain field arises. It may seem like an excellent place to plant them, but it is not recommended due to risks of bacterial contamination. The soil may filter it out, but there is no way to be for sure. Planting and maintaining vegetable gardens require frequent tilling of the soil, watering and the addition of fertilizer, all of which can disrupt the function of septic systems.

Many plants can be planted near septic systems that do not have roots invading the pipes. Remember, take into consideration the expanse of the root system and the location of the septic tank and drain fields. These steps will go a long way to preventing a homeowner’s worst nightmare of damage to the septic system with the accompanying mess and expense.

Timothy Daly is an Agricultural and Natural Resource Extension Agent with UGA Extension Gwinnett. He can be contacted at 678-377-4011or tdaly@uga.edu