Every spring the Merrimack pulls back from its banks and Tyngsborough turns green almost overnight — the low riverside yards first, the high ones about a week behind. 1 Go Green Landscaping takes the town from there with mowing, trimming, edging and spring cleanups, timed to soil that drains slow near the water and quick up on the ridges. There is a rhythm to it: first cut when the maples flower, then week after week through a valley summer that can turn humid inside an hour. The good part comes at the end of an afternoon, stepping back to see the stripes running true across a yard, the beds swept, nothing left behind but the smell of cut grass.