Question
Hi, I read your response regarding the roots of the willow tree.  I actually bought two dwarf weeping cherry trees.  I have a septic system, and planted one of them pretty much on top of the cement, figuring the roots would hit something hard and then travel sideways.  Am I asking for trouble, or are the dwarf versions of these trees too small to cause any damage?   The other tree is planted nearby, but not on top of the septic system.  Thank you for your attention to this matter.

Al in Rhode Island

Answer
There can be a couple of problems with the tree right over the septic tank. All tree roots can invade septic lines if they are planted on top of the lines. They will more than likely not get into the tank since it is generally sealed by the cement lid. They may get into the lines going from the tank. Tree roots will spread about 1 1/2 times the width of the foliage. Depending on the depth of the tank lid, the main problem will be as the tree grows larger the roots will the tree will not be deep enough to get enough water during drought conditions and also since they are restrained by the a tank may not have a system that will anchor the tree during wind storms.

I would move it away from the septic tank. Dwarf versions do not have many problems with the lines as do other trees but planting them right on top of the tank is not a good idea.