When Jim Hachick bought the house at 112 Autumnwood in Amherst 12 years ago, the yard was overgrown. But little by little, it has been transformed into a tranquil space that can also be used to entertain friends. Hachick showed visitors around during the Amherst Garden Walk on July 21. “The pool was already here,” Hachick said. “That is probably the only thing that hasn’t changed.” He even planted the trees, including a tall columnar oak near the pool. At…