Hot Topics: Tree Roots and Septic Systems

Someone pumping out a septic tank.

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Trees can be cause for worry on property with a septic system. This DIYer wants to ensure that no roots are making their way into the drain lines, so they propose to the forum an idea for spreading a root-destroying chemical into the drain field. Wise? As always, the experienced and knowledgeable forum members have opinions.

Original Post: Question About Our Septic System

YaddaYadda Member

Rural Oregon, built in 1993. We moved in 2006. Conventional 1,000 gal. tank with about 300 feet of drain line. No problems apparent.

It has no inspection/distribution box after the line exits the tank. There are five fruit trees and two large fir trees close to the drain lines. I would like to get some copper sulfate or other root-destroying chemical into the drain field just to be sure roots are not going into the lines.

I dug down about three feet and exposed the four-inch line coming out of the tank. It's green, ribbed, and probably 1/4-inch thick. I thought I could drill a hole in this line and somehow install a one- to two-inch pipe about three feet long to soil level, thread a cap on, and use it to get my chemicals into the drain field...eventually.

First thought is to drill the hole, install the pipe (and keep it from dropping more than one inch), seal it, and fill the hole. Does this sound reasonable?

Second thought is to dig down deeper and wider and install this three-foot pipe using a saddle. This will entail a lot of extra digging as I have short arms...and I will have to make a shelf for me to perch my short arms can get down deep enough for the extra digging. Installing a tee is not a consideration.

Any alternatives, suggestions, or comments will be much appreciated.

Vermont Member

You could put the copper sulfate right into the septic tank's outlet and it will go wherever the effluent goes—but no digging or drilling.

How many feet do you estimate you have between the absorption lines and the closest fruit trees?

YaddaYadda Member

Yes, that is the plan—no more digging. The line is exposed.

A local septic company said to add the copper down the toilet and into the tank and then it will work its way into the drain field. Did not want to do that. It would be diluted greatly. Don't know what it would do to the tank flora and fauna, besides.

Some of the fruit trees are right over the drain field and one fir is very close to one line. The other fir is 20 feet away from another line.

AllanJ Member

With no distribution box, the 300-odd feet of leach field line zigzags back and forth. If you put in only a few gallons of solution, it will all soak into the ground within a few feet of being poured in. You need to put in enough copper sulfate solution so some goes all the way to the end.

Pilot Dane Group Moderator

No matter what you do, the chemical will get diluted unless you stop using all water in the house. Everything from the house ends up going into the leach field, so where you add the chemical isn't so important as everything ends up out there in the yard.

YaddaYadda Member

Talked to a local, long-time septic system contractor who advises that the leach field lines themselves have good bacteria inside and not to harm those bacteria/microbes with harsh chemicals. He said that fruit trees he has seen put out roots only 24 inches or so, and because some people irrigate shallow in lieu of deep, it's even less of a problem.

So, some more research is warranted. Thanks for the replies, so far.

Pilot Dane Group Moderator

My opinion is that you don't screw around with your leach field. If trees are a potential problem, the trees go—period. Leach fields are (relatively) easily damaged and expensive to repair. And so much of your home's value rests on a working waste system. Without a working septic system, the house in unlivable and almost impossible to sell.

I have not seen real truths about tree roots other than they go toward what they need. If they need water, they will go deeper. In most residential cases, people don't irrigate enough to control root growth. So, I don't think you can rely on anecdotal hearsay that fruit trees stay shallow.

Numerous times, I have heard people and books say that the tree roots go out as far as the canopy above. But, I have frequently found large roots more than twice the canopy size away. And for depth, I have tried digging up many where my excavator can't dig deep enough to know how far the roots go. I've been down eight to 10 feet and the roots are still big, which is a good indication that they can go very deep.

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