I am bidding on a year-round maintenance contract for a small commercial account. They have several arborvitaes that will need to be trimmed. I normally only do yews, privet, forsythia and hemlock hedges/shrubs. It looks like the arbovitaes been sheared in the past. My question is can gas-fired hedge clippers be used or will that shred them and turn them brown? Would hand shears be better. It will make a big difference in time. Here's a photo of some of them.