Question
I have a 12 year old sycamore tree planted in a border area near my yard.  The roots have invaded my yard, they are on the surface of my yard and are headed to a sidewalk and the foundation of my home.  Can I remove these roots and not kill the tree?  The roots I'd like to cut and dig out are about 25% of the root system.  Thank you.

Answer
The overall concern is the amount of the root system that is cut. The root system extends out beyond the dripline of the foliage maybe another 1/3 the width if the crown. The key is not cutting more then 20 percent of the root system. If you draw a circle on the ground around the tree where the outermost edge of the foliage extends (dripline) and then cut this circle like a pie where the roots were cut and this area is not more then 20% of the circle them the tree will show little effects from the root cutting. Anything above the 20% you can see die back in the foliage crown.
 The closer you cut to the tree trunk the larger the roots are and the likelihood of a bigger percentage of root have been cut. The larger roots also give the tree an anchor against winds.


There are root barriers that will stop the roots from going under sidewalks and foundations. There are chemical barriers --plastic sheeting that has a herbicide in it that will also work to stop roots.

Here is web link to one of these type. http://www.biobarrier.com/biobinfo.html

This material is a thin plastic fabric containing small dots of hard plastic. These plastic dots are impregnated with an herbicide which will not kill the tree but will stop growth of roots as they approach the barrier. This chemical is usually trifluralin herbicide. This herbicide is not absorbed into the plant and translocated; therefore, it does not kill the rest of the plant. It has only low solubility in water and doesn't wash away to other places. This means it will stay in the region of the root barrier and not interfere with the growth of roots elsewhere. This method of root control will involve the least effort (trench one time) and should give many years of protection.

There are other type barriers that can be installed to block the roots. Check with your local nursery for these products.

Here is a link to thes barriers.

http://www.4specs.com/s/32/32-9452.html