I have a customer that wants his hedges trimmed but also wants two(2) 18'-20' hemlocks trimmed as low as possible. I told him the low hedges no problem but I don't usually handle shrubs that have become trees. Can they be brought down to a controllabe size w/out damage to the tree? I have the tools but want to provide good service. Should I refer him to a tree Co.? I would rather say no now than wish I had later. Thanks for any suggestions.