Gardening Sweet Spots
By Donna Hessel
A rain garden is a shallow area on residential or commercial property designed to capture rain runoff and drainage, protecting nearby bodies of water by filtering and soaking water back into the ground before it reaches a drain or sewer.
Why Do We Need Rain Gardens?
In most towns and cities, rainfall and snowmelt drain into an engineered stormwater system of pipes and basins that funnel water, unfiltered, directly into local streams, rivers and lakes. After its trip through the pipes, stormwater is no longer just rainwater. It is hot. Stormwater is warmed as it flows over hot pavement. It is polluted—phosphorous, e-coli and trash are washed off the streets and carried to the creek. And it is huge—a small creek can flow like a river after a rainfall, eroding the banks and muddying the river.
In the river, the polluted runoff poisons fish, plants and other species that depend on them, including us. Most communities get their drinking water from a combination of water drawn from rivers and lakes and from wells. Water polluted with runoff can be more expensive to purify at water treatment plants. Wellwater is only available if rainwater soaks into the ground and recharges the groundwater.
Woods and prairies historically soaked in almost all the rain that fell on them. Concrete soaks in none. People play, boat and fish in the rivers and lakes. If contamination levels are too high, restrictions can be placed on recreational activities such as swimming and fishing. Stormwater is the number one source of pollution in rivers today. Rain gardens are a key feature of eco-friendly landscape design and are gaining credibility and popularity in current garden design.
What Are the Benefits of a Rain Garden?
A rain garden soaks rainwater into the ground quickly. It protects our lakes, rivers and creeks from pollution. It replenishes the groundwater. It creates beautiful gardenscapes and it provides food and shelter for birds, butterflies and beneficial insects throughout the growing season. Plants in rain gardens require less watering during hot summer months because they capture water from the roof and consequently don’t need water from the tap. Water bills may be reduced by using free water from the sky.
How to Design a Rain Garden
- Make it part of the landscape. It should not be a stand-alone feature, but integrated into the rest of the property.
- Choose a shape. Consider composition, screening and circulation.
- Consider style. It can be formal or wild, but should fit with the overall design of the home’s façade.
- Integrate it with other gardens. Consider making a depression within a perennial bed or shrub border.
- Create repetition. Add more than one rain garden, perhaps around each downspout. Or add other water features such as a fountain or birdbath to repeat the water theme and add continuity to the landscape.
- Consider aesthetics and function. Make it user-friendly and attractive by using decorative stone edging, an adjacent seating area, an attractive pathway or garden art.
How to Build a Rain Garden
- Determine the location. The location of a rain garden is critical. If there is a low area or ditch where water collects after it rains, this would be a natural spot for a rain garden. Water can also be redirected from a downspout away from a home to divert water runoff to a rain garden. The rain garden location should be at least 10 feet away from the home so water doesn’t seep into the foundation. The site should receive full sun to partial shade. Avoid locating the garden over a septic tank or near underground utility lines. The ideal size of the rain garden will depend on the area of a home’s roof, the amount of runoff generated, and the soil type. Most rain gardens average between 100 to 300 square feet. The USDA Natural Resources Conservation Service recommends an area that is 7% to 20% the size of the nonporous surface creating the runoff, which is typically the roof.
- Prepare the site. Lawn or other vegetation should be removed and soil type evaluated. Clay soil drains more slowly, while sandy soil drains more quickly. Water should drain within 12 to 48 hours of an average rainfall to keep plants healthy and mosquitoes at bay. A percolation test can determine how quickly soil drains.
- Dig the garden. The next step involves digging a shallow basin 6 to 8 inches deep that slopes from the outer edges to the deepest point at the center. The soil that is removed can create a berm to catch and hold water runoff. The soil in the basin may need to be amended with topsoil or compost to provide a hospitable medium for plants to grow. A pathway of river rocks or installation of an underground pipe may need to be added to guide rainwater from the downspout or other water source into the basin.
- Select plants. This is the fun part. Native plants will provide food and habitat for wildlife and insect pollinators. Perennials and annuals can also be included. Plants should be able to tolerate moisture as well as intermittent dry spells. Sedges, grasses, and rushes with deep root systems will help water seep into the soil. A mix of plants with different foliage, texture, and flowers that bloom at different times will provide season-long interest. More drought-tolerant plants should be planned for bordering the bed perimeter. A list of plant suggestions is included below.
- Install and Maintain the Garden. Plants installed in drifts of 3 to 5 feet will provide greater visual impact. The garden needs to be watered well after planting. Adding an organic mulch will suppress weeds and help to maintain moisture. The garden will need to be watered well during the first growing season until plants are well established. Plants can be pruned according to need and old debris and dead growth should be cleaned out in the spring. Perennials can be divided as needed once plants are mature.
Plants for Rain Gardens
The following lists are recommendations for rain gardens in shade, part shade and sun.
Plants for Shade:
- Ostrich Fern Matteuccia struthiopteris
- Sensitive Fern Onoclea sensibilis
- Wild Ginger Asarum canadense
- Marsh Marigold Caltha palustris
- Jacob’s Ladder Polemonium reptans
- Wild Hyacinth Cammassia scilloides
- Bottle Gentian Gentiana clausa
- Monkeyflower Mimulus ringens
- Early Meadow Rue Thalictrum dioicum
- Sweet Shrub Calycanthus florida
- Sun King Aralia cordata
Plants for Part Shade:
- Canada Anemone Anemone canadensis Swamp
- Milkweed Asclepias incarnata
- Nodding Wild Onion Allium cernuum
- Black Cohosh/Snakeroot Actaea racemosa
- Wild Senna Senna hebecarpa
- Winterberry Ilex verticillata
- Spiderwort Tradescantia virginiana
- Golden Alexander Zizia aurea
- Cutleaf Elderberry Sambucus racemosa‘Lemon Lace’
PerenniPlants for Sun:
- Switch Grass Panicum virgatum
- Beardtongue Penstemon digitalis
- Blue False Indigo Baptesia australis
- New England Aster Symphyotrichum novae-anglia
- Swamp Sunflower Helianthus angustifolia
- Arkansas Blue Star Amsonia hubrichtii
- Swamp Rose Mallow Hibiscus moscheutos
- Culver’s Root Veronicastrum virginicum
- Prairie Dock Silphium terebinthinaceum
- Shrubby Cinquefoil Potentilla fruiticosa
- Rattlesnake Master Eryngium yuccifolium
Rainwater runoff is a huge environmental problem. Runoff water picks up pollutants that a rain garden can filter out: phosphorus and nitrogen from fertilizers; bacteria from animal waste; oil, grease and heavy metals from cars and plain old “dirt.” In a rain garden, sunlight destroys bacteria and viruses. Petroleum is eliminated by bacteria in the soil. Heavy metals are absorbed by soil and mulch. This is in addition to substances that are bad for the environment, such as nitrogen-containing compounds and phosphorous – at rates of over 90%.
Building a rain garden on your property is a simple solution, but it can have a big effect. If you are interested in adding a rain garden to your landscape, check out the references provided for details on how to begin. The Northeast Ohio Master Raingarden group offers a self-directed, online course that I took and found extremely beneficial.
Article Resources:
Garden Design online newsletter – 11-2023 – “Rain Garden Design, Benefits and Plants” by Adam Regn Arvidson
cuyahogaswcd.org – for information on the Cuyahoga Soil & Water Conservation District and its programs
neomasterraingardener.org – for information on the organization, current in-person and online courses on how to build a rain garden. Contact: Kate Chapel, [email protected]
All rain garden photos used with permission from Northeast Ohio Master Raingardener
