When Tree Roots Grow into Sewer Lines

Q. I purchased an older home with a 40 year old maple tree planted near the house. The previous owner told us that the sewer line had backed up due to the roots of the maple growing into the line. She said she had the pipes cleared with an auger and did not have any further problems. But I'm sure it won't be long before those roots go back into the pipe to gain access to that ample supply of water and nitrogen. Is there anything I can do to prevent this besides flushing nasty chemicals down the toilet or cutting down the tree?"

---Luke, who handles the books at Mulhall's Nursery in Omaha

A. Whoa there, Paul Bunyan! It would cost several thousand dollars to have a forty-year-old tree safely cut down; maybe more depending on the proximity of nearby structures and power lines. And that's with you leaving the stump in the ground. Remove the stump and you add to the cost—and insure the final destruction of that sewer pipe.

And don't blame the maple. I spoke with William Eck, an arborist with the Bartlett Expert Tree company, who confirmed my long-held belief that 'the fault is not in our trees, but in our pipes'. In other words, the tree roots didn't break the pipe. Although Bill likes the Marvel Comics image of a massive root crushing the pipe, it is the pipe that broke first. Then came the roots of Groot.

As Bill explains, an older home like this is going to have clay pipe taking wastewater away. A lot of these pipes went into the ground with cracks; others were cracked when tons of dirt were pushed on top to bury them. So the, ahem—'nutrient-rich' water, shall we say—trickles out, one of the fine feeder roots of the tree encounters that wet zone, grows towards the water source and then sends back for silverware, condiments and a napkin when it finds the pipe.

And it's not just old clay pipe. Bill explains that they often see the same thing happen with PVC piping that wasn't sealed properly or that got a hairline crack when the trench was filled back in.

Either way, that little root gets big and strong from all the moisture and nutrients when it does get into the pipe. Then those well-fed and watered roots growing into the crack make it even wider. And once those roots get fully inside, warns Bill, they can grow big and strong very quickly.

Now—cleaning the pipe with an auger is the correct initial response, especially when you consider that these problems are generally only discovered when the roots create a seal inside the pipe and sewage starts backing up into the house.

(Everybody say "Ewwwww!") Ew indeed. But cleaning the pipe is just a temporary solution; new roots are going to grow right back into those existing cracks. And the physical trauma of the cleaning may create new and bigger cracks.

And the chemicals that people flush to kill the roots are not even a one-time solution. Bill says that some of them can be incredibly corrosive. They will kill the roots for a time, but they can also accelerate the destruction of the pipe—and potentially damage indoor plumbing lines as they go from your toidy to the tree. And they can be highly destructive at the end of their journey—causing problems at water treatment plants or killing the biological life that keeps your septic tank functioning correctly.

The best long-term answer is to find a plumber who can insert a flexible pipe with a slightly smaller diameter into the existing pipe. This technology is widely available, but some plumbers balk at narrowing a pipe; and, of course, it has to be legal under local building codes. But it's the most sensible, cost-effective, and sustainable solution.

If it's not legal where you live, you're going to have to dig up and replace the leaky pipe. But you have to be super careful: careless trench digging at this juncture could kill the tree. Then you're back to a three thousand dollar pile of wood chips.

That's why you want the added expertise of an arborist at this point. They can work with the excavator to avoid the most important roots, and professionally prune any roots that can't be avoided. They can also use a device called an 'air spade' to safely expose the roots so they can see exactly what they're doing without the damage caused by actual digging.

Air spades are really cool. I learned about them when I presented at Bartlett's professional tree care symposium during the Philly Flower Show this Spring. It's a tool that uses compressed air to blow away soil and expose the roots of a tree without any digging. They're often used to try and save volcano-mulched trees; the compressed air blows away the smothering layers of mulch and then exposes the top of the root flare if the tree was planted too deeply.

So this is a 'two professional' job: someone to dig up and replace the pipe and an arborist to protect the tree while the work is done. And then be sure and test for leaks before you cover the new pipe. As long as everything is sealed nice and tight, Groot won't be returning any more of your presents to the basement floor.