Conventional wisdom tells us that certain species of trees may be more harmful than others to water and sewage lines especially if planted too close. That is true as far as it goes but all trees have some ability to invade water and sewer lines.
First, tree roots invade mostly through lines that are damaged and in the top 24 inches of soil. Sound lines and sewers have very little trouble with root damage and only at weak points where water is seeping out. The larger, fast growing trees are the biggest problem. Avoid planting these trees near your water service and watch very carefully these kinds of trees near your service.
Roots don't actually crush septic tanks and lines, but rather enter at weak and seeping spots on tanks and lines. Many fast-growing, large trees are considered more aggressive toward water service when finding a water source coming from that service.
Also, older trees can imbed pipes and sewers by growing roots around the pipes. If these larger trees have a structural root failure and topple, these field lines can be destroyed (see photos).
Try to avoid planting these large, fast-growing, aggressive-rooted trees to include Fraxinus (ash), Liquidambar (sweetgum), Populus (poplar and cottonwood), Quercus (oak, usually lowland varieties), Robinia (locust), Salix (willow), Tilia (basswood), Liriodendron (tuliptree) and Platanus (sycamore), as well as many Acer species (red, sugar, Norway and silver maples and boxelder).
Managing Trees Around Sewers and Pipes
For managed landscapes near sewer lines, water-seeking trees should be replaced every eight to 10 years before they grow too big. This would limit the distance that roots grow outside the planting area and the time they would have to grow into and around sewer lines, as well as foundations, sidewalks and other infrastructure.
The University of Tennessee recommends these steps for prevention of tree root damage:
- Plant small, slow-growing trees near sewer lines.
- If faster-growing species are desired, plan to replace trees every eight to 10 years.
- Even slow-growing trees will eventually interfere with sewer lines. These trees must be replaced periodically.
- When building new sewer lines or improving existing lines, consider landscaping plans and potential root intrusion from trees.
If you have to plant a tree, choose small, slow-growing species, varieties or cultivars with less aggressive root systems and to replace them before they get too large for their planting area. There are no safe trees, but by using small, slower-growing trees, sewer lines should be safer from the intrusion of tree roots.
UT also recommends these common trees as planting options near water and sewer lines: Amur maple, Japanese maple, dogwood, redbud, and fringetree.
There are some options if you already have tree root damage to your lines. There are products that contain slow-release chemicals that prevent root growth. Other root barriers can include very compact layers of soil; chemical layers such as sulfur, sodium, zinc, borate, salt or herbicides; air gaps using large stones; and solid barriers like plastic, metal and 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.