On a June evening the steel arch of the Tyngsborough Bridge holds the last of the light while the Merrimack goes dark underneath it, and up on the banks the yards are at their fullest. Greenleaf's Garden Design keeps them in order right through the growing season with mowing, edging, trimming and cleanups that let planted beds read the way they were meant to. A lawn is the frame; when the frame is straight, everything inside it looks intentional. This is a river town of long slopes and old shade trees, so each property gets read for its own light before a blade touches it. The reward is simple — a yard that looks composed at seven in the evening, when people are actually out in it.