ABAG's Sewer Smart Planting Guide
Avoid 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 the sewer main. Responsibility for maintenance of this lateral varies from community to community. But in most cases, the homeowner is responsible for the line at least out to the property line.
Blockages in the lateral are always bad news for the homeowner. Blockages can cause the flow of waste from the home into the sewer main to slow or stop completely. When this happens, sewage can overflow from the lowest opening in the home; for example, a downstairs toilet or shower.
Is my lateral at risk of tree-root invasion?
Depending on the age of your home, your sewer lateral may be made of tile, cast iron, concrete or plastic. Regardless of material, your lateral is filled with water and other nutrients that make it an attractive target for tree roots.
Over the years, earthquakes and shifting soil can cause the lateral to move, often creating cracks. Once roots find moisture, they'll grow right into the pipe itself. That means you may be in for expensive plumbing repairs.
Of course, it's best to avoid this unhappy circumstance by knowing what, where and how to plant trees with avoiding sewer problems in mind! You can help by following the Sewer Smart Tips found elsewhere on this Web site and by following some simple rules for planting above or near your sewer lateral.
First, find your lateral
The first step in observing Sewer Smart planting rules is to have a general idea of where your lateral runs across your property and into the sewer main.
One of the best ways to find your lateral is to refer to the survey documents you likely received when you purchased your home. If you don't have these documents, your city planning or public works department can most likely provide copies for you to view. In some cities, they're even available online.
No need to despair if you don't have them, though. You can determine the general location of your sewer lateral - good enough for planting purposes -- by following these three steps:
STEP 1: Find the point where the lateral leaves the house by locating the cleanout.
STEP 2: Find the point where the lateral leaves your property and crosses into the street by:
- Locating an "S" or other similar mark in or on the curb.
- Locating a second cleanout at the property edge, in the sidewalk or roadway. This cleanout may be under an access cover marked with an "S" or "Sewer."
STEP 3: Draw an imaginary line between the two above points. Sewer laterals normally run in straight lines.
What to Plant, What Not to Plant
Once you've determined the general location of the lateral on your property, you should avoid planting - or maintaining - any plants, bushes or trees that are likely to grow into or otherwise foul your lateral.
For more information on where-to-plant considerations, visit the International Society of Arboriculture (ISA)'s Webpage, Avoiding Tree & Utility Conflicts, at trees are good.
The type of tree you plant is also important for preventing future sewer problems. Depending on the species of tree, 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.
Planting appropriate types of trees is of critical importance. Tree roots tend to grow toward sources of water - including sewer pipes. 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. However, some particularly ambitious trees can extend roots far beyond the drip line, or limits of their canopies, as they pursue water sources.
There are a number of "problem" trees that should be avoided if sewer laterals and other underground utilities are a concern. These problem trees include poplars, willows, figs, rubber trees and large eucalyptus trees. Two of the more troublesome trees are the fruitless mulberry and the Modesto ash.
For an extensive guide on tree selection, visit Cal Poly's site and select "low" for "Root Damage Potential" along with the other tree attributes you seek.
More Sewer Smart Planting Tips
After you select a tree, follow proper planting procedures. Be sure to dig a deep enough hole, but not too deep. If your hole is too shallow, the tree's roots will be more likely to spread horizontally making it more likely that they'll meet, and possibly penetrate, sewer pipes and other underground utilities.
However, if your hole is too deep, the tree's root crown will be buried and disease and decay may result. According to the ISA, "It's better to put a $100 tree in a $200 hole than to put a $200 tree in a $100 hole."
For more on tree planting, visit tree care.
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. A properly selected, planted tree will be a beautiful and healthy addition to your home's landscaping and won't cause headaches -- or backups -- in the years ahead.
More Sewer Smart Planting Information
Your local nursery may also be a good source of planting information. For a list of nurseries and garden centers in the San Francisco Bay Area that are participating in the Be Sewer Smart program, visit the California Association of Nurseries and Garden Centers.
For more useful, local tree resources, visit the City of Oakland's Public Works Agency tree program.
Still more tree information can be obtained from the University of California Cooperative Extension program.
For more specific information on desirable and undesirable plantings in your community, contact your city's public works department or your local sanitary district.