Question
I have a conifer hedge along my driveway. Some of the roots have pushed up the
tarmac. If I cut off these roots will the conifers survive? ( the conifers have been
growing for around 20 years )

Answer
You can dig a trench along the driveway and cut the roots and this will stop the damage. You can cut up to 1/4 of the root system of a tree without damaging the tree--the closer the tree is to the drive the more roots will be cut. Tree roots grow in the first 12-18 inches of soil so you will need to trench down to this depth to sever most of the roots. I would install a root barrier along the drive this will stop the growth of the roots. Here is a web link to these barriers.  http://www.4specs.com/s/32/32-9452.html