Rain Gardens - Solving drainage problems
 by Ann English

 

Storm water runoff and poor drainage are difficult conditions for most gardeners and homeowners. These seemingly dismal situations are actually ideal environments for certain plants. You can turn a problem area into a low-maintenance, beautiful garden watered only by the rain; a "rain garden" that will manage storm water runoff for both aesthetic and environmental advantage.

Retention Basin Retention Basin Spring of 2004

 

THE BUILDING PROCESS IN 4 EASY STEPS

First, identify the area that is low lying or is otherwise seasonally sodden. Typically, it is an area that may look muddy, eroded, or it is an area you have tried gardening or grassing to no positive end. Locate your garden just above the puddling area if at all possible or as close to the source of the water causing the puddling problem. This will solve the puddle and identify the water source for your rain garden.

Second, decide on a design theme or concept for the area that fits with the rest of your garden. This will be your organizing plan for your solution, and will allow you to make decisions from your many ideas as to what is appropriate for the particular site. It can be very simple (a view from a room) or an elaborate metaphor (a space for healing) that allows you to make decisions regarding what to place where.

Third, define your rain garden edges with either hard materials or a mowed path. The edges will make it easier for everyone to visually understand your design. A good edge sets off a garden bed nicely.

Fourth, choose the right plants for wet conditions. The right choice will thrive in this situation which may be deadly for other plants naturally adapted to drier conditions. This will solve the puddle and identify the water source for your rain garden.

DESIGN TO SOLVE STORM WATER PROBLEMS

Recently, a project at Cedar Shoals High School (CSHS) in Athens, Ga., transformed a barren, muddy, acre-sized storm water retention basin into a low-maintenance wildlife sanctuary. A simple form, a logarithmic spiral of trees and shrubs, fronted by a variety of wetland grasses and perennials, was used to create a more visually pleasing scale in this space that every visitor sees when arriving at the school.

A mown edge reinforces the spiral arrangement of the plants and paths in the CSHS rain garden. The majority of the garden is populated with herbaceous species, which were both planted and "volunteered" once the maintenance crews stopped applying pesticides to the basin to kill the existing vegetation. Airflow was allowed to remain unfettered by the plant arrangement and this, combined with the increased bird and frog populations, has substantially reduced the number of mosquitoes that previously dominated the area.

CULTURAL REQUIREMENTS & MAINTENANCE

In general, plants for a rain garden should be selected for their ability to tolerate winter "wet feet," site sun conditions and the typical summer dry spells that we experience in the South. One advantage of the type of plants that thrive in swampy conditions is their ability to grow well in compacted, anaerobic conditions. The right plant for the right place is the key to success in this type of garden. All of the CSHS plants will grow in the conditions of the basin, thriving in the fluctuations of moisture capacity and in the full sun that the area experiences, with no need for supplemental water, fertilizer or pruning once established. Most were installed as small plants, allowing them to grow up and adapt to the conditions of the basin as they mature. A plant may be a naturally-occurring swamp plant, but if it develops into a large nursery-grown specimen in a non-swamp environment, it may not survive the change of condition.

In a rain garden, plants are positioned by water requirements. The plants that need more moisture are planted in the wettest areas, while those that need slightly drier conditions are planted according to the classifications of "aquatic," "emergent," "bog," "intermittent bog" or "occasionally flooded" cultural requirements. In addition, the CSHS Rain Garden plants are mostly native to Southeastern flood plains and swamps. The river birch (Betula nigra) is a woodland edge species, and the swamp tupelo (Nyssa aquatica) is a swamp tree; both can tolerate the pollution of storm water runoff from the surrounding five acres of parking lots.

The entire acre is maintained by quarterly mowing of the paths and six three-hour work days by student groups in the course of the year. Thus, this garden, despite its size, is an extremely low-maintenance and low-cost solution to an extreme environmental problem. A rain garden installed in a residential setting will also be low maintenance, requiring seasonal weeding and annual mowing but not a lot else to keep it looking beautiful.

DIVERSITY IS KEY

At Cedar Shoals, a variety of grasses and perennials were installed. This encouraged a diversity of wildlife to populate. Native grasses (Panicum virgatum and Chasmanthium latifolium) and perennials (such as Helianthus angustifolius and Iris virginica ) are in the "emergent aquatic" areas. Perennials, such as swamp mallow (Hibiscus moschuetos), swamp milkweed (Asclepias incarnata) and yellow flag (Iris pseudacorus), are planted in areas that are submerged under a few inches of water for long periods of time. Joe-Pye weed (Eupatorium purpureum) and ironweed (Vernonia noveboracensis) also produce beautiful late summer displays and in addition to their ability to live in wet places, they are quite drought tolerant.

RAIN GARDENS AT HOME

To adapt the ideas shown in this one-acre plan to the individual homeowner scale, simply reduce the number of plants to fit your space. A rich diversity of plants is desirable in all solutions. Most residential scale rain gardens should minimize woody plants used, as those tend to reduce air movement in the landscape and increase the chance of mosquito breeding to occur. Start with a design arrangement you like, then find the right plants to fit your space and conditions. Maintain a clear edge to your garden area and think of a pleasing succession of color and texture for interest through the year. Many people dream of a garden that is inexpensive to create and maintain, while providing a wealth of beauty. Additional positive attributes of such a garden would enhance the environment by attracting birds, butterflies and other wildlife, and by improving water quality. All of this and more is possible with the establishment of a rain garden.

Swamp hibiscus (Hibiscus coccineus) Chasmantium latifolia Initial planting

(Click on any photo to enlarge)

If you would like more detailed construction information, three online sources are: lowimpactdevelopment.org, raingardens.org and mninter.net.

Great websites for information on native Southeastern trees and shrubs are:
ncwildflower.org and plantnative.org.

- Story reprinted from Georgia Gardening Magazine Vol. 3, No.6.


Ann English is a landscape architect in Maryland working for the Montgomery County Department of Environmental Protection in the Watershed Management Division. She has taught planting design at the School of Environmental Design at UGA and has taught the Sustainable Tools class for the Sustainable Landscapes program at George Washington University since 2007.



 

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