Tree Roots in Your Sewer Line or Yard: What to Do

Few tree problems are as expensive to ignore as roots. A sewer backup in a finished basement, a driveway slab lifted two inches, a lawn you cannot mow without hitting knuckles of maple root: every one of these traces back to a tree doing exactly what trees do, which is hunt for water and oxygen wherever the soil offers them. Thompson Tree Care and Landscaping is not a plumbing company, and we will be clear throughout this guide about which parts of the fix belong to a plumber. What we can tell you, after more than a decade of assessing and removing trees across St. Louis, Kirkwood, Florissant, and Belleville, is which trees cause the trouble, when the tree itself is the real problem, and what to do about roots above and below ground.

How do tree roots get into a sewer line?

Roots are not drills. They cannot punch through intact PVC or cast iron. What they can do is sense the moisture and warm, nutrient-rich vapor escaping from a pipe that is already leaking, and grow toward it. Once a hair-thin root tip finds a gap, it slips inside, drinks, and thickens. Over a few seasons that root becomes a mat that catches paper and grease until the line is blocked.

The gaps are the problem, and older St. Louis housing stock has plenty of them:

• Vitrified clay laterals with hub-and-spigot joints every few feet, standard in homes built before the 1970s across the city and inner-ring suburbs. Every joint is a potential entry point once the mortar or gasket fails.
• Orangeburg pipe, a tar-impregnated wood-fiber pipe used in many mid-century homes. It softens, deforms, and blisters with age, and roots find it easily.
• Cracked cast iron in pre-war homes, where corrosion opens seams along the bottom of the pipe.
• Settled or offset joints in any material, where the ground has shifted and pulled a connection apart.

The warning signs are familiar to anyone who has lived through it: drains that slow a little more each month, gurgling toilets, sewage odors in the yard, backups that return a year or two after the last "fix," and a strip of lawn over the lateral that stays greener than everything around it because the roots are being fed.

Which trees are the worst offenders?

Any tree will use a leaking pipe, but a handful of fast, shallow-rooted, water-loving species account for most sewer and driveway complaints in the St. Louis area:

• Silver maple — the single most common culprit in older neighborhoods. Fast growing, enormous, and rooted right at the surface.
• Willow — legendary for finding water; a weeping willow will travel a long way for a wet joint.
• Cottonwood and poplar — aggressive, shallow, and huge.
• Sycamore — a river-bottom tree by nature, with roots to match.
• American elm — the old street-tree standard, with wide-spreading surface roots.
• Sweetgum — shallow, heaving roots that also lift sidewalks.
• Bradford pear — not as far-reaching, but planted so densely near foundations and driveways that it shows up constantly. Our guide to Bradford pear problems and removal covers the rest of its bad habits.

Distance matters less than most homeowners think. Tree roots live mostly in the top 12 to 18 inches of soil and spread one to three times the width of the canopy, so a 40-foot-wide maple in the backyard can have feeder roots under the front-yard lateral. If the tree is within 15 or 20 feet of the pipe run, assume the roots are already there.

What fixes the pipe, and what only buys time?

This part is the plumber's job, but it helps to know what you are buying when the estimates come in.

Temporary Relief

• Camera inspection is the essential first step. It shows exactly where the roots are entering, what the pipe is made of, and whether the line has sagged or collapsed. Insist on seeing the video.
• Mechanical root cutting with a cable auger clears the blockage in an afternoon. The roots regrow from the stubs, often within a year.
• Hydro-jetting scours the pipe walls more thoroughly than cutting, but it is still a haircut, not a cure.
• Copper sulfate or foaming root killers flushed down the line kill the roots inside the pipe and slow regrowth for a season or two. They do nothing for the gap the roots came through, and repeated heavy doses stress the tree and are hard on septic systems and waterways.

Permanent Repair

• Cured-in-place pipe lining (CIPP) inserts a resin-saturated liner that hardens into a jointless pipe inside the old one. No trench, no joints, no entry points. It requires the old pipe to still hold its shape.
• Pipe bursting or open-trench replacement is the answer when the lateral has collapsed or deformed. It is also the moment to decide what happens to the tree, since a trench through its root zone may do as much damage as removal.

In most of the St. Louis metro, the lateral from the house to the main is the homeowner's responsibility, not the sewer district's; check with your district or municipality to be sure. Some area municipalities run lateral repair or lateral insurance programs funded by a small fee on the water or sewer bill, and it is worth a phone call before you pay for a replacement out of pocket.

When is the tree itself the fix?

A sealed pipe solves the sewer problem regardless of the tree. But there are situations where the tree should go, either because sealing is not practical yet or because the tree is causing more than one problem:

• A large, water-seeking species (silver maple, willow, cottonwood, sycamore) sits directly over the lateral or within 10 to 15 feet of it, and you are not ready to line or replace the line. The roots will return after every cutting.
• Backups have recurred after two or more root cuttings. At that point the annual plumber's visit costs more than the tree is worth, and every backup risks a flooded basement.
• The same tree is also crowding the foundation, hanging over the roof, or heaving the driveway. Our guide to trees that are too close to the house walks through that decision.
• The lateral is being replaced by open trench, and the trench will sever most of the roots on one side of the tree anyway.

That last point deserves emphasis. Cutting a few large roots close to the trunk to "keep them out of the pipe" is not a middle path. Roots within about five times the trunk diameter anchor the tree, and severing several of them on one side can leave a mature tree with nothing holding it against the next storm. A tree that starts leaning after root damage is a removal, not a repair; see our guide on when a leaning tree is a problem. If the roots have to be cut, plan on removing the tree and replanting something better suited to the spot.

What about surface roots heaving the driveway, sidewalk, or lawn?

Above-ground root trouble is the same tree doing the same thing for a different reason. St. Louis clay compacts hard, holds water, and starves roots of oxygen a foot down, so roots grow where the air is: right at the surface. Add a driveway or sidewalk slab that traps moisture underneath, and roots run along its edge, thicken, and lift it.

What helps, roughly in order of how often we recommend it:

• Stop fighting the lawn. Grass will never win under a mature maple. Convert the root zone to a two- to three-inch mulch bed or a shade groundcover, and the trip hazard, mower damage, and bare patches disappear.
• Never shave or grind exposed roots to make mowing easier. Every cut is a decay entry point on a root the tree depends on.
• Do not bury them. Piling six inches of topsoil over surface roots smothers them; the tree responds by sending new roots up through the fill.
• Install root barriers when a driveway or walk is being repoured. A barrier 18 to 24 inches deep along the slab edge deflects new roots downward. It is far cheaper to install during the concrete work than after.
• Root pruning only with an arborist, only on the side away from the house, and only on roots small enough that the tree can spare them. Our certified arborist can tell you which roots those are and which would compromise the tree.
• Remove the tree when the slab is being replaced, the species is one of the offenders above, and the tree is otherwise unremarkable. A silver maple lifting a driveway will lift the new driveway too.

How do you remove tree roots after the tree is gone?

Removing a tree removes the engine, not the plumbing. What happens to the roots afterward depends on where they are.

Around the stump: stump grinding chews the stump and the major roots near it 6 to 12 inches below grade, which is enough to reseed the lawn, plant a bed, or pour a walk. Grinding wider than the stump itself, sometimes called root chasing, follows the larger surface roots outward and is priced by the extra time. Typical St. Louis-area stump grinding runs $100-$400 per stump, with large silver maple and sycamore stumps at the top of that range.

Farther out: the rest of the root system stays in the ground and decays over three to seven years. The roots stop growing the moment the tree is cut, so there is no need to dig them out for their own sake. Sprouting species such as silver maple, cottonwood, and Bradford pear may send up suckers from the remaining roots for a season or two; mowing them off ends it.

Inside the pipe: removing the tree does nothing for roots already in the sewer line. Those still have to be cut or jetted out by a plumber, and the entry gap still has to be sealed, or the next tree over will find it. Sequence the work so the plumber goes in after the tree is down and the stump is ground, not before.

For the tree itself, typical St. Louis-area tree removal costs $300-$2,500 depending on size and access. Thompson Tree Care and Landscaping estimates are free, we are licensed and insured, and we offer senior and veteran discounts.

What should you plant near sewer lines and driveways instead?

The fix that lasts is putting the right tree in the right place. Near laterals, water lines, driveways, and walks, choose small trees with modest root systems, and keep anything that will grow into a large shade tree at least 20 feet from the pipe run. Good choices for St. Louis yards include:

• Serviceberry — spring flowers, edible berries, 15 to 25 feet, roots that stay home.
• Eastern redbud — a Missouri native with a compact root system and a 20-foot crown.
• American hornbeam — tough, slow, and well behaved near hardscape.
• Flowering dogwood — shallow but small, and happiest in the part shade a driveway strip often provides.

If you are not sure whether the tree over your lateral is a problem waiting to happen or just a good shade tree in the wrong conversation, we will come look at it. Call (314) 712-3035 or request a free estimate, and we will tell you plainly whether the roots, the pipe, or both need attention.

Frequently Asked Questions