WHAT IS A RAIN GARDEN?

A rain garden is desigend to allow rain water to infiltrate into the ground rather than simply wash into storm drains or surface water. The garden itself is placed mid-slope between the run-off source and a storm sewer, ditch, or stream. A run-off source may be an impermeable surface, such as the roof of a house, a driveway, or even a parking lot. It may simply be an upslope area that drains to a lower area or a stream.

Rain gardens serve as a bio-swale. In the process of intercepting the runoff, plants in the rain garden may remove excess nutrients from fertilizer granules that would otherwise be deposited directly into streams,  that then make their way to lakes, rivers, or the ocean.

Rain gardens have increased in popularity across the country, due, in part, to small grants from state governments, and also due to educational efforts through extension offices and other educational channels.

DESIGN

A rain garden is sized based on the amount of water it will receive in a short period of time. This is usually calculated by using the area that is draining into the rain garden, and includes the amount of rainfall expected. For example, if a 200 square foot driveway is draining into the rain garden, and an inch of rain fall is typical, then these are the numbers used for the calculation.

Most rain gardens are only 3-6 inches in depth. The soil must be well-draining. Otherwise, it must be amended to permit adequate drainage.

Hardwood mulch is used on the surface of the rain garden. This aids in moisture retention and has less of a tendency to float when the rain garden is wet.

Rain gardens must be well-draining, and thus are not likely to provide mosquito egg-laying habitat. A well-designed rain garden will completely drain in a 24-hour period.

PLANTS

Rain gardens can accomodate a variety of plants, from trees and shrubs to herbaceous perennials. They may be native plants or non-natives, although many people prefer to use native plants. The main criteria for plant selection is a wide range of soil-moisture tolerance, from wet to dry. Plants should be selected for hardiness. Most states have internet resource materials to aid in planning rain gardens.

RELATED WEBSITES

North Carolina State Cooperative Extension, Backyard Rain Gardens. http://www.bae.ncsu.edu/topic/raingarden/

Rain Gardens of West Michigan. http://www.raingardens.org/Index.php

Fort Wayne's Rain Garden Program. http://www.catchingrainfw.org/index.php?option=com_content&view=article&id=44&Itemid=2

California shrubs and Trees for Rain Gardens. http://www.native-raingarden.com/californiatreesandshrubs.html