Question about trimming/pruning Leland Cypress
I have to trim back several mature Leland Cypress trees that were neglected by their owners and have grown about 35 feet high and have spread horizontally such that they're growing over my gutters and roof. The trees are about 10 years old. I received a strangely wide variety of opinions regarding how much trimming can be done to these trees. Note that I'm talking about trimming or shaping the horizontal growth (not the tops or reducing their height). Almost all sources say that this should be done in late February or early March, just as it begins to warm up in Georgia. However, I've had all manner of advice regarding how much can be sheared or pruned off the side-ways growth: One person said you shouldn't trim more than about 4 or 5 inches, all the way to one who said that Lelands can tolerate "extensive shearing" to the point of shearing like a hedge.
Does anyone know the real scoop about Leland Cypress trees? I would ideally like to reduce their horizontal girth at least a couple of feet on each side (they are currently massive -- probably 12-15 feet wide at their widest point of growth), but don't want to harm the trees.