For two weeks each April the cherry trees in Branch Brook Park turn the north end of Belleville into something out of a painting, and every lawn in town suddenly has an audience. BELLEVILLE LANDSCAPING COMPANY spends that stretch getting yards ready to keep up — first mowings, beds cleared of the winter's leavings, edges cut back clean along the sidewalks. These are close-set Essex County properties where inches matter, so trimming is done by hand around fences, steps and hydrant strips. Through summer the mowing keeps its schedule, and by fall the leaf cleanups run right out to the curb. A small yard, kept even, can carry a whole block.