Quick facts
A rain garden is a planted low area that allows rainwater runoff to soak in from hard surfaces like roofs, driveways, walkways and parking lots. A rain garden:
- Removes pollutants from water before it enters surface waters.
- Prevents erosion by holding soil in place with its deep roots.
- Attracts birds and butterflies.
- Requires little watering and maintenance once established.
The benefits of rain gardens
Whether you live in the city or along a lake or river, managing stormwater runoff is important.
Rooftops, roads, driveways and sidewalks are hard surfaces that prevent rainwater and melting snow from reaching the soil and soaking into the ground. These hard surfaces also collect nutrient-rich yard and pet waste, oil and radiator fluid from autos, and other debris and pollutants.
Runoff:
- Washes debris and pollutants away, often directly into lakes, rivers and wetlands.
- Erodes soil and carries it into our surface waters.
- Can affect aquatic life if warm runoff enters lakes and rivers directly. In summer, runoff is often warmed as it flows over hard surfaces.
Rain gardens:
- Collect stormwater runoff and prevent it from flowing directly into lakes, rivers and wetlands.
- Allow runoff to soak into the soil so sediments settle and plants absorb nutrients.
- Filter out pollutants from water before entering the groundwater.
- Prevent erosion by holding soil in place with their deep roots.
- Attract birds and butterflies.
- Require little watering and maintenance once established.
Design and placement
Rain garden designs can be simple or elaborate, depending on your gardening interest and experience. Before you start digging, it's best to sketch a design. You'll need to consider:
- Location of the garden.
- Size you need.
- Shape you want.
- Type of soil you have.
- Plants you’d like to include.
- How much runoff you typically have.
- You may need more than one rain garden to accommodate the runoff.
First, determine areas of your property that are suitable for a rain garden. These will generally be low areas that are a recommended distance away from other features.
Rain gardens should be:
- 10 feet or more away from buildings to prevent foundations and basements from being damaged by water.
- 35 feet or more away from septic system drain fields.
- 50 feet or more away from drinking water wells and well away from utility lines.
Call the Digger’s Hotline (800) 242-8511 to locate electrical, gas or telephone lines.
Test the soil in areas that are both suitable and near the sources of runoff. For an analysis of the type of soil you have and its nutrient content, send a sample to the U of M Soil Testing Lab.
The kind of soil in your rain garden is very important. The soil needs to be porous enough to soak up water within 48 hours to prevent plants from drowning and mosquitoes from breeding. This is also the standard shortest period between two rainstorms.
To simply test a soil’s ability to absorb water:
- Dig a wide hole 10 inches deep and fill it with water.
- If the water disappears within 48 hours, the site is suitable for a rain garden.
- If your first site fails the 48-hour test, test the soil at other potential rain garden sites on your property.
Rain gardens can be designed in any shape. Crescent or kidney shapes are attractive. A long, narrow rain garden may be better if you're placing it between structures, such as a house and sidewalk.
The size of your rain garden will depend upon the size of the roof, driveway or other hard surface being drained.
- Typical rain gardens range from 100 to 300 square feet in size.
- Gardens will handle the runoff from a hard surface that is about three times their size.
- For larger surfaces, more than one rain garden may be needed to handle the runoff. For example, large roof tops may need a rain garden near each down spout.
Choose plants that:
- Are appropriate for the soil type in your rain garden.
- Will tolerate standing water for up to 48 hours.
Many native plant species are well suited for rain gardens. If you are constructing a rain garden near a lakeshore or riverbank, you may be required to use native plants, depending upon local ordinances. Check with your local Soil and Water Conservation District.
Table: Rain garden plants
Botanical Name | Common Name | Height | Moisture* | Exposure** | Native Habitat | Color | Bloom Time |
---|---|---|---|---|---|---|---|
Aquatic Plants: grown in less than 12" of water, soil is always saturated | |||||||
Carex comosa | bottlebrush sedge | 24-42" | s,w,um | S | marsh, peatland, lake edge | green | May-June |
Carex crinita | fringed sedge | 30-42" | s,w,um | S | marsh, swamp, lake edge | green | May-June |
Carex lacustris | lake sedge | 24-36" | s,w,um | S | marsh, swamp, lake edge | green | May-June |
Carex stricta | tussock sedge | 24-36" | s,w,um | S | swamp, marsh, peatland | green | May-June |
Eleocharis palustris | spike rush | 6-24" | s,w,um | S | wetland, wet prairie | brown | August |
Iris versicolor | blue flag iris | 24-36" | s,w | S, PS | marsh, peatland, lake edge | blue | June-July |
Juncus effusus | soft rush | 24-48" | s,w,um | S | swamp, marsh, lake edge | brown | July-Aug |
Sagittaria latifolia | common arrowhead | 24-42" | s,w | S, PS | lake edge, marsh | white | July-Aug |
Scirpus acutus | hardstem bulrush | 36-108" | s,w | S | lake edge, marsh | green | June-July |
Scirpus validus | softstem bulrush | 36-108" | s,w | S | marsh, swamp, lake edge | brown | July-Aug |
Non-Aquatic Plants: Wildflowers or forbs | |||||||
Agastache foeniculum | fragrant hyssop | 24-40" | um,ud | PS | prairie, savanna | blue | June-Oct |
Allium stellatum | prairie wild onion | 12-24" | um,ud | S, PS | prairie, savanna | pink | July-Aug |
Anaphalis margaritacea | pearly everlasting | 6-18" | um,ud | S, PS | prairie, savanna, woodland | white | July-Sept |
Anemone canadensis | Canada anemone | 12-24" | w,um | PS, Sh | prairie, marsh, swamp | white | May-July |
Arisaema triphyllum | jack-in-the-pulpit | 8-24" | w,um | PS, Sh | woodland, forest | green | April-June |
Asclepias incarnata | swamp milkweed | 36-48" | w,um | S | prairie, marsh, lake edge | lavender | June-Aug |
Asclepias tuberosa | butterfly flower | 12-24" | ud | S, PS | prairie, savanna | orange | June-Sept |
Aster novae-angliae | New England aster | 24-48" | w,um | S, PS | prairie, marsh, swamp | blue | Aug-Oct |
Boltonia asteroides | boltonia | 48-96" | w,um | S, PS | prairie, marsh, swamp | white | Aug-Sept |
Dalea purpurea | purple prairie clover | 12-24" | ud | S | dry prairie, savanna | purple | June-July |
Echinacea angustifolia | purple coneflower | 24-36" | um,ud | S, PS | prairie, savanna | purple | July-Aug |
Eupatorium maculatum | Joe-Pye weed | 24-48" | w,um | S, PS | wet prairie, marsh, swamp | purple | July-Sept |
Gentiana andrewsii | bottle gentian | 18-30" | w,um | S, PS | prairie, marsh, lake edge | blue | Aug-Oct |
Geum triflorum | prairie smoke | 6-12" | um,ud | S | dry prairie, woodland | purple | April-June |
Helianthus maximiliani | Maximilian sunflower | 24-108" | w,um | S | swamp, prairie, lake edge | yellow | Aug-Oct |
Liatris pychnostachya | prairie blazing star | 24-36" | w,um | S | prairie, marsh, lake edge | purple | July-Sept |
Lobelia cardinalis | cardinal flower | 24-48" | w,um | S, PS | prairie, marsh, lake edge | red | July-Oct |
Lobelia siphilitica | great blue lobelia | 20-30" | w,um | S | prairie, marsh, lake edge | blue | July-Oct |
Monarda fistulosa | wild bergamot | 24-48" | um,ud | S, PS | prairie, savanna, woodland | lavender | July-Aug |
Rudbeckia hirta | black-eyed Susan | 3-4' | um,ud | S, PS | prairie, savanna | yellow | June-Oct |
Rudbeckia laciniata | wild goldenglow | 36-108" | w,um | S, PS | prairie, swamp, lake edge | yellow | July-Aug |
Thalictrum dasycarpum | tall meadow rue | 36-72" | w | S, PS | prairie, swamp, lake edge | cream | June |
Uvularia grandiflora | large-flowered bellwort | 12" | um | PS | deciduous forest | yellow | May |
Verbena hastata | blue vervain | 24-60" | w,um | S, PS | prairie, marsh, swamp | blue | June-Sept |
Zizia aurea | golden Alexander | 12-36" | w,um | S, PS | prairie, savanna, woodland | yellow | May-July |
Graminoides (grasses and grass-like plants) | |||||||
Acorus calumus | sweet flag | 36" | s,w | S, PS | marsh, peatland, lake edge | yellow | July-Aug |
Andropogon gerardii | big bluestem | 36-72" | um,ud | S, PS | prairie, savanna, woodland | purple | July-Sept |
Bouteloua curtipendula | side oats grama | 1-2' | um,ud | S | prairie, savanna, woodland | red | July-Sept |
Bouteloua gracilis | blue grama | 6-18" | um,ud | S | prairie, savanna | purple | July-Sept |
Bromus kalmii | Kalms brome | 24-36" | w,um,ud | PS, Sh | prairie, savanna, woodland | green | June-July |
Calamagrostis canadensis | bluejoint grass | 36-72" | w,um | S, PS, Sh | prairie, marsh, swamp | green | July-Sept |
Carex bebbii | Bebbs sedge | 24-36" | w,um | S | marsh, swamp, lake edge | green | May-June |
Carex comosa | bottlebrush sedge | 24-42" | s,w,um | S | marsh, peatland, lake edge | green | May-June |
Carex lacustris | lake sedge | 24-36" | s,w,um | S | marsh, swamp, lake edge | green | May-June |
Carex pensylvanica | Pennsylvania sedge | 6-8" | um,ud | S, Sh | dry to mesic forest | brown | May |
Carex scoparia | pointed broom sedge | 6-30" | w | S | marsh, wetland, lake edge | tan | May-June |
Carex sprengelii | Sprengel's sedge | 12-24" | um,ud | S | woodland, forest | green | June-July |
Carex stricta | tussock sedge | 24-36" | s,w,um | S | swamp, marsh, peatland | green | May-June |
Carex vulpinoidea | fox sedge | 12-36" | w,um | S | swamp, marsh, lake edge | green | May-June |
Eleocharis palustris | spike rush | 6-24" | s,w,um | S | wetland, wet prairie | brown | Aug |
Elymus hystrix | bottlebrush grass | 24-48" | w,um,ud | PS, Sh | forest, woodland, lake edge | green | June-July |
Glyceria canadensis | rattlesnake manna grass | 24-36" | w | S | marsh, peatland, lake edge | green | July-Aug |
Glyceria grandis | tall manna grass | 36-60" | w | S | swamp, peatland, lake edge | green | July-Aug |
Hierochloe odorata | sweet grass | 12-24" | w,um | S | lake edge, marsh, prairie | green | May-June |
Juncus effusus | soft rush | 24-48" | s,w,um | S | swamp, marsh, lake edge | brown | July-Aug |
Juncus tenuis | path rush | 6-12" | w,um | S, PS, Sh | swamp, marsh, lake edge | brown | July-Aug |
Koeleria macrantha | June grass | 12-24" | um,ud | S | prairie, savanna, woodland | green | June-July |
Panicum virgatum | switchgrass | 36-72" | w,um,ud | S | prairie, swamp, lake edge | purple | June-Oct |
Schizachyrium scoparium | little bluestem | 24-48" | um,ud | S | prairie, savanna, woodland | amber | July-Sept |
Scirpus atrovirens | green bulrush | 36-48" | w | S | marsh, swamp, lake edge | brown | June-July |
Scirpus cyperinus | wool grass | 36-48" | s,w,um | S | marsh, swamp, lake edge | brown | June-July |
Scirpus validus | softstem bulrush | 36-96" | s | S | lake edge, marsh | brown | June-Aug |
Sorghastrum nutans | Indian grass | 24-72" | w,um | S, PS | prairie, savanna, woodland | amber | July-Sept |
Spartina pectinata | cord grass | 36-72" | w,um | S | prairie, marsh, lake edge | yellow | Aug-Oct |
Shrubs and small trees | |||||||
Amelanchier laevis | serviceberry | 15-25' | um,ud | PS | forests, fields, clearcuts | white | April-May |
Aronia melanocarpa | black chokeberry | 3-6' | w,um,ud | S, PS | lake edge, forest, swamp | white | May-June |
Cornus alternifolia | pagoda dogwood | 15-25' | um,ud | PS | forest, swamp | white | May-July |
Cornus racemosa | gray dogwood | 5-15' | um,ud | PS, Sh | forest, fields, lake edge | white | May-July |
Cornus sericea (stolonifera) | red-osier dogwood | 6-12' | w,um,ud | S, PS, Sh | forest, wetland, lake edge | white | May-July |
Corylus americana | American hazel | 8-15' | um,ud | S | forest, wetland, lake edge | purple | March-April |
Diervilla lonicera | bush honeysuckle | 2-4' | um,ud | PS, Sh | woodland, forest, clearcuts | yellow | June-July |
Prunus virginiana | chokecherry | 20-30' | um,ud | S, PS | forest, woodland | white | May |
Sambucus pubens | red berried elderberry | 4-8' | um,ud | PS, S,Sh | dry to moist forest | white | May |
Symphoricarpos albus | snowberry | 4-6' | ud | S | forest, woodland | whitish | May-July |
Viburnum atropurpurea | downy arrowwood | 6' | ud | S, PS | woodland, forest, clearcuts | white | May-June |
Viburnum lentago | nannyberry | 12-18' | um,ud | PS | forest, swamp, lake edge | white | May-June |
Viburnum trilobum | highbush cranberry | 5-15' | w,um | S, PS | forest, swamp, lake edge | white | June |
* Moisture Zone Key: ud = upland-dry (dry, well-drained soils); um = upland-mesic (soil is moist, but not wet); w = soil is wet, occasionally standing water; s = shallow water most of the time
** Exposure Key: S = full sun, PS = partial sun, Sh = shade
Building and planting
Construction can begin once garden size, shape, location and plants have been decided.
- Lay out a rope or hose in the desired shape to use as a guide for digging.
- The depth may vary from 4 to 10 inches.
- For best infiltration, the bottom of the rain garden should be level.
- If your garden is placed on a slope, use the soil from digging to create a berm on the downhill side of the rain garden.
- Remove excess soil from the site.
Reviewed in 2018