If you want to practice the ancient water-finding art of dowsing, reach for a weeping willow (Salix spp.) branch. The water-seeking weeping willow will find water, even when you don't want it to. Hardy in U.S. Department of Agriculture plant hardiness zones 2A through 9A, weeping willows have aggressive roots that invade septic systems and drain pipes.
Water Loving Roots Cause Havoc
Weeping willow trees put out thin feeder roots that grow into small cracks in a tank or pipe, and, once inside, they will multiply, clogging up the system. As the roots grow, they also will make a tiny crack bigger, causing further damage. Weeping willow roots also affect the leach or absorption field, the area below the septic tank where the damp, nutrient-rich soil causes the fast-growing willow tree to flourish.
Detecting a Problem
It's not hard to figure out when your septic system isn't functioning properly. The first sign is a distinctive and less than pleasant odor coming up from toilets in the house. If the problems isn't fixed, sewage will start backing up. Willow roots growing into pipes, septic tanks and leach fields can cause the system malfunction, but there are other causes of malfunction, too. If you're not sure of the source of the problem, consult a professional to diagnose the system.
Kill the Roots, Not the Tree
You can slow root damage to a septic system with chemical tree root herbicides. Root killer herbicides are designed to kill the small feeder roots growing inside pipes and tanks without killing the tree. Use 8 pounds of root killer for a 1000-gallon tank by pouring it directly into the septic tank. You also can add root killer to the system through a toilet and get rid of any roots in the pipes at the same time, just use an additional 4 pounds of root killer for every 100 feet of pipe distance.
If Something's Gotta Give
When willow roots find a water source near a leaking pipe or a crack in the septic system, they grow thicker and stronger in that area. Root killers provide a temporary fix, but the roots regrow as long as the tree is alive. If you have ongoing problems, consider removing the tree and replanting with something less aggressive. Removing a full-size weeping willow will require a professional tree removal team.
Avoid Problems With Good Spacing
Plant weeping willow trees at least 50 feet away from the septic system, or, if you are putting in a new septic system, make sure it is at least 50 feet away from any willow trees. This 50 feet is a minimum spacing and even with this distance you could run into problems as the tree matures. The best way to prevent weeping willow roots from getting into a septic system is by not planting willows in residential areas.