Do you have any general recommendations about how far apart any trees that we plant need to be from the septic system?


I’m considering planting some trees or shrubs as a privacy screen at the edge of my property. I’m concerned about root systems and encroachment upon our septic system which is on that side of the house. Do you have any general recommendations about how far apart any trees that we plant need to be from the septic system to prevent harm to the septic system? One option that I was considering, to be on the safe side, was perhaps doing American Holly shrubs since I read that their root systems may be more shallow. How far from the septic would you suggest American Holly needs to be? Do you have any other septic safe privacy evergreens that you might recommend?


Jonathan Foster, Home Horticulture Outreach Professional

You’re right to consider the impact of root systems on septic system leach fields, so kudos to you for your forethought. Improper planting can cause major headaches down the line, as roots damage and interfere with the engineering of the field (please see this previous Ask an Expert reply from my colleague, Liz Stanley).

The Clemson Univ Extension has a nice article on this topic here. For woody plants, they have the following advice:

“Woody plants are mostly larger shrubs and trees that have woody stems and other woody plant parts that do not die back to the ground in winter. These plants are much more likely to cause serious damage to drain fields with their root systems. Trees with very aggressive root systems that should be avoided include willows, red and silver maples, beeches, birches, elms and poplars. Some trees with less aggressive root systems include cherries, crabapples, dogwoods, hemlock and oaks. To reduce the associated financial risk and emotional stress of a failed system, plant trees at least as far away as their estimated root spread at maturity. There are two methods used to estimate tree root spread. One rule of thumb is that roots extend out from the tree two to four times the diameter of the canopy. Another is that tree roots spread out one to three times the height of the tree. These estimates should be considered a bare minimum, and to reduce the risk, the trees should be planted even further away from the drain field.

Shrubs with less aggressive root systems should never be planted any closer than 10 feet and small less aggressive trees no closer than 20 feet from the drain field. Planting these less-aggressive species, such as boxwoods, hollies or arborvitae towards the drier ends of the drain lines may also reduce the risk for problems down the road.” [emphasis mine]

I would not recommend boxwood as an alternative, though, due to the species’ role in the spread of the invasive box tree moth.

Happy gardening.