First speak to the contractor and try to work out an agreement. If they don't complete the work, don't pay them. If you paid them and they don't agree with your agreement on settlement, sue them in court after sending a final demand letter. My guess is that this is a small claims court matter, which means you file suit against the defendant landscaper in the county within which the landscaper is located. I'm sure they aren't too far away. Now if you're asking about suing a worker for someone whom you hired, you sue the company or person with whom you have a relationship.