· Brent Wilson's Answer
· Hi Rose - As crape myrtles are top-rooted and not water-lovers, and most septic lines are buried quite deep, they are actually good tree selections to plant near a septic field or tank. The Dynamite Crape Myrtle grows up to 15 in width and the root system could extend 5 to 10 feet beyond the perimeter of the branch canopy at maturity.
Regarding the planting distance from the foundation of a home, I think you can get away with keeping the trunk spaced at least 10 feet away. This is more to keep the tree from growing up against your house than to protect your foundation. At my previous home, I had two massive Natchez crape myrtle (25 feet tall x 20 feet wide) growing no more than 5 feet away from the basement foundation walls. These trees were there when I bought the home and were probably 20 years old at the time. The roots never caused any problem. I did have to keep the backside of the canopies pruned to keep it off the house.
Regarding septic field lines and tanks, just to be on the safe side, I would suggest a minimum of 20 feet away.
Avoid planting trees such as riverbirch, weeping willow, maples and other water-lovers near septic fields.
Hope this info was helpful ad let me know if you have further questions,