Sizing and Shaping a Rain Garden
Size a rain garden against the hard surface that feeds it: the portion of roof or paving draining to the basin decides how much water arrives in one storm, so the basin needs enough surface area to hold that runoff briefly while it soaks away. A shallow, saucer-like profile helps water spread evenly, so it ponds only briefly between storms rather than stagnating. A gentle berm along the downhill edge helps hold water in, and a level overflow route gives excess somewhere safe to go during exceptional rain. Shape the outline to fit existing paths and planting, since an irregular, natural curve usually sits more comfortably in a garden than a formal rectangle.