Building A Rain Garden | UMN Extension

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1. Home
2. Yard and garden
3. Lawns and landscapes
4. Landscape design
5. Rain gardens

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.

Open all | Close all Plus sign (+) if content is closed, 'X' if content is open. Location

BEFORE YOU DIG, in Minnesota, contact Gopher State One Call.

Several factors should determine the site of a rain garden:

• It should be located to collect water above the area where rain currently collects or runs off into a body of water. The objective is to slow or collect the run-off in the rain garden and allow the water time to percolate into the soil.
• Locate the rain garden at least 10 feet away from buildings to prevent water damage to foundations and basements.
• Locate it 35 feet or more away from a septic system drain field to avoid interrupting or impeding the drain field’s effectiveness.
• Chemicals, run-off from roofs, atmospheric deposits, and various nearby activities on the land can all pose contamination risks to drinking water. Protecting your well from potential contaminants helps ensure that your household has safe, clean drinking water.
  • If you plan to apply fertilizers or pesticides to your rain garden or anticipate contamination from other sources, locate the rain garden at least 150 feet from your drinking water well, as recommended by the Minnesota Department of Health for agricultural chemicals.
  • While Minnesota Rules don’t specify a setback for rain gardens, a minimum of 20 feet is required between a well and drainage features, such as French drains (MN Rule 4725.4450). For sensitive wells, this distance increases to 40 feet.

Plus sign (+) if content is closed, 'X' if content is open. Shape and size

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.

Plus sign (+) if content is closed, 'X' if content is open. Test the soil

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:

1. Dig a wide hole 10 inches deep and fill it with water.
2. If the water disappears within 48 hours, the site is suitable for a rain garden.
3. If your first site fails the 48-hour test, test the soil at other potential rain garden sites on your property.

Plus sign (+) if content is closed, 'X' if content is open. Choose plants

Choose plants that:

• Are appropriate for the soil type in your rain garden.
  • Get a soil test.
• 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

This list includes plants for the wetter parts of the rain garden, as well as the upland dry portion.

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	Kalm’s 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	Bebb’s 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 the 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.

Contributors: Laura Irish-Hanson and Brenna Finley, Extension educators; Julie Weisenhorn, retired Extension educator

Reviewed in 2025

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