Rain gardens and drainage basics

What a rain garden does

A rain garden is a shallow, level-bottomed bed that collects runoff from a roof, driveway or other hard surface and holds it while it soaks in. University of Minnesota Extension sets the target at draining within 48 hours. That keeps plants from drowning and mosquitoes from breeding, and it matches the usual gap between storms.¹

Building one, step by step

1. Pick the spot Choose a place in full or partial sun, at least 10 feet from the house so water stays away from the foundation, and at least 35 feet from a septic drain field. The bottom should sit at least 2 feet above the water table.¹²
2. Call 811 Have buried lines marked. Ohio law requires two working days’ notice before digging.³
3. Test the drainage Dig a wide hole about 10 inches deep and fill it with water. If it drains within 48 hours, the spot works. If not, test somewhere else.¹
4. Size it Most home rain gardens are 100 to 300 square feet. One garden can handle runoff from a hard surface about three times its own area, so a 100-square-foot garden handles about 300 square feet of roof or pavement. A big roof may need a garden at more than one downspout.¹
5. Dig it level Dig 4 to 10 inches deep with a level bottom. On a slope, use the soil you dig out to build a low berm on the downhill side.¹
6. Plant by zone and mulch Put plants that tolerate standing water in the lowest part and drier-soil plants around the edges, then cover bare soil with 2 to 3 inches of hardwood mulch.¹²
7. Plan the upkeep Penn State Extension points out that a common reason rain gardens fail is that nobody planned how to maintain them.⁴

Ohio natives for the wet middle

These handle wet soil and are on ODNR’s wetlands, floodplains or wet woods lists.⁵⁶⁷

• Swamp milkweed Asclepias incarnata perennial, 3–5 ft
• Northern blue flag iris Iris versicolor perennial, 2–3 ft
• Cardinal flower Lobelia cardinalis perennial, 4–5 ft
• Great blue lobelia Lobelia siphilitica perennial, 1.5–4 ft
• Fox sedge Carex vulpinoidea sedge, up to about 3.5 ft (40 in)
• Common boneset Eupatorium perfoliatum perennial, 4–6 ft
• Spotted Joe-Pye weed Eutrochium maculatum perennial, 4–7 ft
• White turtlehead Chelone glabra perennial, 1–3 ft

Ohio natives for the drier rim

The edges dry out between storms. These take average to dry soil.⁸⁷

• Little bluestem Schizachyrium scoparium grass, 2–4 ft
• Purple coneflower Echinacea purpurea perennial, 3–4 ft
• Switchgrass Panicum virgatum grass, 3–7 ft
• Golden Alexanders Zizia aurea perennial, 1–2 ft
• Ohio spiderwort Tradescantia ohiensis perennial, 2–3 ft
• Wild bergamot Monarda fistulosa perennial, 2–4 ft

Other drainage basics

For low spots that stay wet, NC State Extension lists four options: an underground drainage system, raised beds, regrading, or a rain garden.²

Give walks and driveways a slight slope so water runs into planted areas, and use permeable surfaces for walks and patios where you can so water soaks in.²