In all states, a homeowner may trim the branches or roots of a neighbor's tree up to the property line. You must, however, stay on your property to do the trimming, and and make sure not to injure or cut down the neighbor's tree. Perhaps the five neighboring property owners will want to share the cost of hiring a tree service to trim the tree's runners back to the tree owner's property line. To maintain good neighborly relations, check in with the tree owner before starting to trim. The tree owner may be grateful to have some help, because tree trimming can be an expensive proposition.

If the tree itself has grown into the boundary lines, ownership may be shared among the neighbors, in which case the responsibility for the tree shifts, and you may need to share removal costs. And if the trees are interfering with power lines or sewers, the local utility company might help with the task and cost of removal.