Why roots get in
Older sewer laterals are clay tile, laid in short sections with a joint every few feet. The joints were never watertight, and they loosen as the ground shifts. A root hair finds the moisture, gets inside, and grows into a mass that catches paper and solids.
Silver maples and willows are known for it, but any big tree near the line will do it. Towns of mid-century houses on lots with mature trees see the most of it. Olivette is one, and so are the old streets of St. Charles near Main Street and Frenchtown. Cast iron can let roots in at its joints too, and a crack in any kind of pipe is an open door.
Cutting them out
A cable machine fitted with a root-cutting blade is run through the line. The blade is sized to the pipe and shears the roots off at the wall. A jetter with a root-cutting nozzle does the same job with water and flushes the pieces out. Either way the line drains again the same day.
Keeping them out longer
Cutting doesn't kill the root, and the cut ends grow back. Two things stretch the time between visits:
- A foaming root killer applied after cutting. The foam fills the pipe and kills the roots inside it without harming the tree.
- Cutting on a schedule, before the line backs up. Once roots have shown up, a yearly cabling is the usual plan.
Your own history is the guide. If the line backed up 14 months after the last cut, have it done at 12.
When cutting stops being the answer
If roots are back within a few months, or the camera shows the pipe has cracked or separated where they come in, cleaning is no longer buying much. The repair is to line the pipe or dig up and replace that section.
Before you pay for that yourself, check whether your city runs a sewer lateral repair program. The City of St. Louis and many St. Louis County municipalities do, funded by a yearly fee on the property tax bill, and they pay toward fixing a broken lateral. They don't pay for root cutting.
Common questions
How often do roots need to be cut out of a sewer line?
Once a year is the usual plan after roots have shown up. Fast-growing trees close to the line can need it sooner. Your own history is the best guide: book the next cut a couple of months short of the gap between your last two backups.
Does root killer work?
A foaming root killer applied after a cut slows the regrowth inside the pipe. It won't open a line that is already blocked. Crystals flushed down a toilet run along the bottom of the pipe, while roots mostly come in at the top and sides of the joints.
Do I have to cut down the tree?
No. Taking the tree out doesn't remove the roots already in the pipe, and the joint that let them in stays open to the next tree. The lasting fix is to the pipe. Lining it or replacing that section leaves no joint for roots to find.
Will the city's sewer lateral program pay for root cutting?
No. Lateral programs pay toward repairing a broken pipe, and they treat cabling and root cutting as ordinary upkeep. Chesterfield, Olivette and the City of St. Louis all say so in their rules. If roots have cracked or separated the pipe, the repair itself may qualify, so keep your invoices.