Question
I am required by our local municipality to connect my house to the public sewer.  This means that I have to dig within 5' of the dripline of my 30+ foot tall blue spruce.  There are large tree roots showing above ground, so I know that I will be disturbing the root system with this sewer installation.  Can I a) cut the roots as I go by or b) try to save the major roots by working through them?  As a side note, can I remove the portions of the roots that are showing above ground?  They are approx 3"-4" in diameter.  Thanks,

Answer
The general rule about cutting root systems is you can get away with cutting about 1/3 of the system without severely damaging the tree. To figure the 1/3 go out from the tree trunk until you clear the overhang of the branches-- this is called the drip line of the tree. Draw a circle around the tree at the drip line - then mark the line that will be dug. IF the part of this circle that wil be cut off is more than 1/3 of the circle then you could expect some die back of foliage. The good news conifers can with stand more damage than hardwoods. Conifers have a tap root that will compensate for lateral root damage when it comes to water and food uptake. The majority of e roots are within the first couple of feet of soil so you will cut through the root system. More than likely with a sewer pipe you will not be able to dig under the roots easily. I would go ahead and dig the trench but make sure the equipment is NOT driven on the tree side so that you do not disturbed any of the left root system. I would not cut any of the exposed roots in the remaining circle of roots. You can cover the exposed roots as long as you do not use more than 2 inches af sand placed over the roots. When you have finished I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good. Apply the fertilizer just before a rain event and you will not need to water. I hope this answers your question if not ask again.