Tree Roots in Sewer and Water Lines

Conventional wisdom says that the roots of certain tree species may be more harmful to water and sewage lines than others, especially if planted too close to these utilities. That wisdom weighs out as far as it goes, but all trees have some ability to invade water and sewer lines.

Root Egress

Tree roots invade mostly through damaged lines installed in the top 24 inches of soil. Sound lines and sewers have very little trouble with root damage, and then only at weak points where water seeps out.

Aggression toward water service in many fast-growing, large trees is spawned by the discovery of a water source coming from that service. As is the case with any living thing, a tree will do what it must to survive. Roots don't actually crush septic tanks and lines, entering instead through weak and seeping spots on tanks and lines.

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It's important to closely watch these aggressive trees when they grow near your sewage service, or avoid planting them altogether:

• Fraxinus (ash)
• Liquidambar (sweetgum)
• Populus (poplar and cottonwood)
• Quercus (oak, usually lowland varieties)
• Robinia (locust)
• Salix (willow)
• Tilia (basswood)
• Liriodendron (tulip tree
• Platanus (sycamore)
• Many Acer species (red, sugar, Norway and silver maples, and boxelder)

Managing Trees Around Sewers and Pipes

For managed landscapes near sewer lines, replace water-seeking trees every eight to 10 years before they grow too big. This limits the distance roots grow outside the planting area and the time they have to grow into and around sewer lines as well as foundations, sidewalks, and other infrastructure.

Older trees can embed pipes and sewers by growing roots around the pipes. If these trees experience a structural root failure and topple, these field lines can be destroyed, so it is important to keep a close eye on these as well. To help prevent tree root damage that will eventually interfere with sewer lines:

• Plant small, slow-growing trees near sewer lines.
• Plan to replace trees every eight to 10 years if you desire faster-growing species.
• Periodically monitor and replace even slow-growing trees.
• Thoroughly evaluate landscaping plans for potential root intrusion when improving or building new sewer lines.
• Consider Amur maple, Japanese maple, dogwood, redbud, and fringetree, common trees recommended for planting near water lines.

Options exist if you already have tree root damage to your lines. Products containing slow-release chemicals to stymie further root growth are helpful. Other root barriers include:

• Densely-compacted layers of soil
• Chemical layers such as sulfur, sodium, zinc, borate, salt or herbicides
• Air gaps using large stones
• Solid barriers such as plastic, metal, or wood.

Each of these barriers can be effective in the short term, but long-term results are difficult to guarantee and can significantly harm the tree. Seek professional advice when using these options.