Question
I received a purple robe locust as a house warming gift 2 yrs ago and planted it about 10 ft. from the back of my house in the city and 6 feet from my driveway.  I was told it grows to about 20-25 feet.  I can already see that it is a fast growing tree.  Can it affect city sewer lines and will I be in trouble a few years from now?

Answer
Purple globe locust is grafted onto the root stock of black locust which is known to cause sidewalk and driveway lifting. Black locust is not recommended to be planted closer then 3.5 meters or about 12 feet from sewer lines. The root system of tree is about twice the width of the spread of the foliage. Most of the larger roots are within the dripline of the outer foliage. If it can be moved to a place further from the lines it would be better to move it now while it is small then wait until it grows larger.