Q: Yearly we use a product that says it clears our septic tank lines of tree roots. Can these products really make a difference?

A: I am neither a plumber or soil scientist so I can’t answer your question with any expertise. Copper sulfate is a time-honored method of clearing roots but I can find no scientific research that says it actually works.

Nonetheless, this factsheet from Oklahoma describes its use.

Controlling Tree Roots in Sewer Lines
with Copper Sulfate

If you want to try it, do not flush the chemical down the toilet or down any drain inside the house. The crystals will likely settle to the bottom of the tank, where they don’t do you any good and they could inhibit the vital bacterial action inside the tank.

Instead, find the distribution box that connects the main tank to the several drain field lines and put the chemical there, following the label directions.

Dr. Larry West, who IS a soil scientist says:

“The basic question is if roots interfere with the onsite drainfield lines. I have heard reports that they do, but they are very infrequent. I think at one time roots may have been a problem, but that was at the time that clay tiles with spaces between the tiles were used for the drainfield. Roots had an opportunity to get into the line through the spaces between tiles.

“Current drainfields may or may not have a pipe and if they have a pipe, it is solid plastic with holes on the bottom side that is surrounded by gravel or a man-made aggregate (at least 4 inches on top and bottom and 16” on each side). Root growth is not my specialty, but I do not think large tree roots would grow around the pipe to the bottom and up through holes to clog the line, especially since there is probably wastewater ponded in the trench (not a failure; this is the way the system works).

“I have no real data to support this hypothesis, but I have excavated a few systems under grass, and there were no grass roots in the pipe or even in the gravel. There was a concentration of roots at the trench-soil interface since there was abundant water and nutrients (the grass is greener over the drainfield). I would guess tree roots would behave similarly.

“I also have an issue with loading the soil with copper which is a hazardous metal.

“The bottom line is that the manufacturers of the root control products and many other products that “extend the life of” or “improve” septic systems are using peoples fear and lack of understanding of their on-site system to sell products. The products are normally not harmful and may even have a limited beneficial effect. However, in most cases they are not necessary.”

A more permanent idea would be to dig a root barrier trench between the trees and the septic system. Rent a trench digger machine, dig the trench 18 inches deep and insert 18 inch wide aluminum flashing edge-wise. Carefully backfill the trench with soil and the metal will repel roots for many years.