DIVISION OF AGRICULTURE RESEARCH & EXTENSION Agriculture and Natural Resources University of Arkansas System

FSA9533

Rain Gardens and Stormwater

Katie Teague What is stormwater? constructed wetlands, open space County Extension Agent ­ conservation and land development Agriculture/Water Quality When precipitation falls to the ordinances. Homeowners and property ground or snow melts, it either managers can also manage storm water percolates into the soil or moves Mike Daniels in a manner that is relatively inexpen­ across the land or an impervious sive, pleasing to the eye and beneficial Professor - Water Quality surface as stormwater until it to the environment through the use of and Nutrient Management reaches a creek or stream, eventually rain gardens. flowing to a natural storage area John Pennington such as a pond, a lake or a reservoir. What is a rain garden? County Extension Agent ­ In some cases, stormwater is stored As their name implies, rain Agriculture/Water Quality temporarily in small depressions until it can infiltrate or evaporate. gardens are cultivated areas created to collect stormwater runoff. A rain Mark Brown Stormwater runoff is a natural garden is a landscaped depression County Extension Agent ­ process, but it can be greatly altered that collects rainfall from impervious Water Conservation by development, which creates large areas such as roofs, driveways or areas of impervious surfaces such as parking lots and blends in seamlessly parking lots, roofs, buildings, roads, with other landscaping. Thus, they are sidewalks and driveways. Impervious really smaller-scale bio- retention surfaces prevent infiltration and basins that fit perfectly around houses create greater volumes and flow and lawns. The garden’s flat bottom velocities of storm water runoff for and porous soil help distribute rain a given area. This, in turn, increases water evenly across the planted area, the potential for storm water to collect allowing the water to slowly soak into and transport pollutants such as the ground within 48 hours after the sediment, nutrients, bac teria and rain stops. Appropriately designed petroleum-based products to streams rain gardens will not increase mos­ and ultimately to lakes and oceans. quito populations since mosquitoes It also creates greater potential for cannot complete their breeding cycle flooding in urban areas when small in this length of time. natural drainage areas can no longer While they are beautiful, low- accommodate stormwater flows due maintenance additions to your yard, to increased runoff volume and rain gardens also provide important flow velocities. environmental benefits. Landscaped To protect our waterways from with native plants, rain gardens pro ­ Arkansas Is polluted stormwater, the United States vide habitat that attracts local wild ­ Our Campus Environmental Protection Agency now life, including butterflies and birds. By has laws in place that require certain catching and allowing rainwater to municipalities to manage and control slowly percolate into the soil, rain Visit our web site at: stormwater runoff through measures gardens recharge groundwater https://www.uaex.uada.edu such as bio-retention basins, bioswales, supplies and decrease stormwater

University of Arkansas, United States Department of Agriculture, and County Governments Cooperating runoff. Rain gardens are designed and constructed • Enhancing the beauty of yards, neighborhoods in such a way that the soil in the garden can filter and businesses through beautiful landscaped and remove any pollutants from the captured areas. stormwater, thereby protecting the quality of • Providing habitat for birds, butterflies and our groundwater. beneficial insects. • Reducing flooding and drainage problems in Rain gardens can vary in size and shape and yards and communities. contain an infinite arrangement of plants and colors • Sustaining creek flows during dry periods. to fit into any landscape. Rain gardens have been used at businesses, in neighborhoods, schools and • Reducing the flow intensity of creeks during parks. They can be placed virtually anywhere where storm events. runoff can be collected. How do you build a rain garden? How do rain gardens work? The first step to constructing a rain garden is to Rain gardens are designed to capture develop a plan that includes location, size and shape stormwater and to hold it long enough to allow (layout), porous media selection, mulch selection and interaction with soil but not long enough to create plant selection. habitat for mosquitoes. Rain gardens capture Site Selection stormwater by being placed downslope of drainages from impervious surfaces. Once stormwater is Rain gardens can be placed just about anywhere collected, it is stored temporarily in the rain garden but must be placed at a lower elevation than the where it interacts with plants and soil before runoff entrance and the surrounding land. The draining to groundwater or evaporating. In this installation of a rain garden will most likely require manner, rain gardens can function like temporary, some shallow excavation. To avoid damage to under­ miniature wetlands. Wetlands can remove pollutants ground utility lines and serious injury, contact by slowing the flow of stormwater to allow soil to filter pollutants via adsorption and entrapment, while plants can uptake some pollutants such as nutrients and metals in a process known as phyto-remediation. Also, oxygen imported into the soil by wetland plants can help microbes transform and degrade pollutants before the water drains to ground­ water or is released to natural drains. In this manner, rain gardens become more than a beautiful land­ scape feature, they become an effec­ tive way of capturing, reducing and remediating stormwater runoff.

What are the environmental benefits of rain gardens? Rain gardens provide a number of relatively low-cost benefits to the environment including: • Removing pollutants including sediment, fertilizers, pesticides, automotive fluids and metals from stormwater. • Increasing water infiltration and recharging groundwater supplies. Figure 1. Examples of rain gardens. Figure 2. Schematic cross section of a typical rain garden (Rain garden detail created by Jeff Huber, University of Arkansas Community Design Center). your local utilities to ensure your location does not fourth time and observe how long it takes the coincide. Other tips for locating rain gardens include: water to soak out of the hole. If the soil is already saturated from rain, you may not have to fill it • The rain garden should be at least 10 feet three times. Use the following guidelines to from the house to avoid interaction with the determine suitability: foundation. • Do not place rain gardens directly over septic • Rapid percolation: Water drains out of the hole systems or lateral lines. within an hour; soil may not hold water long • Avoid areas where water already ponds as this enough for establishment of vegetation. Organic indicates poor infiltration. matter amendments such as compost or peat • Place rain gardens in full or partial sun. moss needed. • Selecting gently sloping land will reduce • Moderate percolation: Water drains out of the exca vation efforts. hole within eight hours; ideal for effective rain garden establishment. An extremely important consideration for • Slow percolation: Water does not completely drain determining the suitability of your site is to ensure within 24 hours; site may be too wet, clayey or that you have adequate infiltration and water low for effective rain garden. Additional digging movement through the soil. You can do a simple and soil amendments necessary. percolation test to determine how quickly water moves through your soil. Dig a hole about 12 inches Size and Shape deep and about 6 inches in diameter. A post-hole digger is good for this. Fill the hole with water Once you have determined a location that is free three times and allow it to thoroughly saturate of utility lines, then determining the size and shape the surrounding soil. Fill the hole with water a should follow. Rain gardens can be any size and shape, but here are a few guidelines that can Table 1. Native Arkansas plants for rain gardens. Plants improve performance: shown in gray either can take a good amount of shade or need afternoon shade. • Total area should be at least 10% the size of the Perennials and Grasses impervious area from which runoff is being Allium cernuum Nodding onion collected, such as a roof or driveway, with 30% Amsonia tabernaemontana Willow leaf blue star being optimum. Andropogon geradii Big bluestem • The depression area of the garden should be Andropogon glomeratus Bushy bluestem excavated to six to eight inches below the original soil surface or deeper with greater Asclepias incarnata Swamp milkweed slope. The bottom of the garden should be flat. Aster oblongifolius Fragrant aster If the percolation test indicated slow water Aster paludosus Prairie aster movement, then dig four to six inches deeper Aster sagittifolius Arrow leafed aster and remove that soil and save for berm Aster turbinellus Violet prairie aster construction. Break up the soils on the bottom Baptisia sphaerocarpa Yellow wild indigo of the bed with a rototiller, shovel or pitchfork. Carex species Many sedges Backfill with soil mixture described below. Chasmanthium latifolium Northern sea oats or Indian • A berm four to eight inches above the top of the woodoats planting bed should be constructed around the Chelone species Turtle head perimeter of the garden. Eupatorium species Joe Pye weed As far as shape, rain gardens can be any shape Gelsemium sempervirens Carolina jessamine including kidney, crescent, rectangular, circular or Helianthus angustifolius Narrowleaf sunflower square. Its shape can be constructed to uniquely fit Hibiscus coccineus Texas star hibiscus your landscape and be pleasing to your eye. Hibiscus mos. v. lasiocarpus Red eye mallow Soil Mixture Ilex verticillata Winterberry holly Iris fulva Copper iris The results of your percolation test can help Iris virginica Blue flag guide you on how to amend the soil that is used as Liatris pycnostachya Gayfeather backfill. For rapid infiltration, mix removed soil Lobelia cardinalis Cardinal flower with equal mixture of an organic amendment such as compost or peat moss. For moderate percolation, Lobelia siphilitica Blue cardinal flower you may not have to amend for water movement. Malvaviscus arb. Turkʼs turban However, adding 25% to 40% compost or peat moss v. drummondii may be advantageous to the long-term soil fertility Muhlenbergia capillaris Pink muhly grass and plant life. For slow percolating soils, remove Osmunda cinnamomea Cinnamon fern and use the soil collected from the additional Osmunda regalis v. speciosa Royal fern digging for the berm. Mix equal parts sand, organic Panicum virgatum Switchgrass material and original topsoil (four to six inches) and Parthenium integrifolium Wild quinine backfill to desired garden depth. Penstemon digitalis Beardtongue Plants Penstemon tenuis Gulf Coast penstemon Physostegia species Obedient plant Rain gardens can be as colorful, beautiful and Polemonium reptens Jacobʼs ladder unique as your creativity allows. Hundreds of Polygonatum biflorum Solomonʼs seal plants can work in rain gardens. However, native Rudbeckia maxima Giant coneflower perennial flowers, grasses and shrubs that can tolerate both drought or moist soil conditions Schizachyrium scoparium Little bluestem should thrive in your garden. They’ll also entice Silphium species Rosinweed butterflies, hummingbirds and other nectar and Sisyrinchium angustifolium Blue eyed grass berry feeders to visit and provide better disease Solidago species Goldenrod resistance. These local plants tend to be well- Tripsacum dactyloides Eastern gamma grass adapted to a range of regional conditions and will Vernonia arkansana Arkansas ironweed flourish without chemical fertilizers and pesticides. Vernonia lettermanii Lettermanʼs ironweed A list of select native plants for Arkansas is listed Vernonia missurica Missouri ironweed in Table 1. Veronicastrum virginicum Culverʼs root Woody Plants Summary Alnus serrulata River alder Rain gardens are becoming a popular landscape Amorpha fruticosa Evening primrose feature in Arkansas because they are relatively Aronia arbutifolia Red chokeberry inexpensive, beautiful and provide many environ­ Aronia melanocarpa Black chokeberry mental benefits. They are a great way for home­ Asimina triloba PawPaw owners, businesses, neighborhoods and communities Betula nigra River birch to address stormwater runoff and ensure that our Callicarpa americana Purple beauty berry surrounding creeks and streams are clean, healthy Cephalanthus occidentalis Buttonbush and functional. Chionanthus virginicus Fringe tree Cornus drummondii Rough leaf dogwood Cornus racemosa Gray dogwood Itea virginica Virginia sweet spire Leitneria floridanum Corkwood Lindera benzoin Spicebush Magnolia virginiana Sweet bay magnolia Myrica cerifera Southern wax myrtle Nyssa sylvatica Black gum Quercus michauxii Swamp white oak Rosa palustris Swamp rose Salix species Willows Sambucus canadensis American elderberry Taxodium distichum Bald cypress Viburnum dentatum Arrowwood Viburnum nudum Shonny haw Viburnum prunifolium Blackhaw viburnum

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KATIE TEAGUE and JOHN PENNINGTON are county extension Issued in furtherance of Cooperative Extension work, Acts of May 8 agents - agriculture/water quality in the Washington County Extension and June 30, 1914, in cooperation with the U.S. Department of Office in Fayetteville. MARK BROWN is county Extension agent - Agriculture, Director, Cooperative Extension Service, University of water conservation in the Pulaski County Extension Office in Little Arkansas. The Arkansas Cooperative Extension Service offers its Rock. DR. MIKE DANIELS is professor - water quality and nutrient programs to all eligible persons regardless of race, color, national origin, management in Little Rock. All are with the University of Arkansas religion, gender, age, disability, marital or veteran status, or any Division of Agriculture. other legally protected status, and is an Affirmative Action/Equal FSA9533-PD-12-11N Opportunity Employer.