What you need to know to avoid causing planting-related sewer problems:
Your home's sewer is connected to the sewer "main" (a large pipe often running under the street) via a pipe known as a "lateral" that extends from your home, across your property and into a sewer main. The homeowner is responsible for the maintenance of this lateral out to the property line. Blockages in the lateral are always bad news for the homeowner as they can lead to slow downs or complete stoppages of the flow of waste from the home and into the sewer main. When either of these situations occurs, an overflow of the home's own sewage out of the lowest opening in the home (downstairs toilet, shower, etc.) is the likely result.
Is My Lateral at Risk of Tree Root Invasion?
No matter what the construction, your lateral is filled with water and other nutrients that make it an attractive target for tree roots. Movement of the lateral over the years due to shifting soil may have created openings in it that give tree roots lucrative targets and points of entry to the pipe itself. Once roots find a moist spot caused by sewer lines, they'll grow right into the pipe itself. And that means you may be in for expensive plumbing repairs.
In addition to planting locations, the type of tree you plant is also important to preventing future sewer problems. Depending on the species of tree involved, the "safe" distance from your lateral varies. For example, roots of some Poplar trees have been known to reach into sewer lines nearly 100 feet away.
If you're making additions to your home's landscaping, you can save yourself headaches and money by choosing trees with deeper root systems. In particular, avoid planting trees with shallow, spreading root systems near your lateral. Tree roots, in many cases, mirror somewhat the tree's above-ground canopy, growing in a "pancake" several feet thick below the surface. The problem trees to avoid include poplars, willows, figs, rubber, fruitless mulberry and Modesto ash.
Remember, there are other non-sewer reasons to plan before you plant. Trees in the wrong places can also wreak havoc with your home's foundation, driveways, sidewalks and other structures.