Why Do It

raingarden.jpgRain Gardens have two major environmental benefits. Rain gardens slow and retain runoff, which reduces flooding and erosion associated with peak storm flows. Second, they filter runoff, removing pollutants and improving water quality. In addition, they are attractive additions to the landscape, relatively inexpensive, and easy to install.

In South Portland, rain gardens are a recommended approach to meet Drainage Plan permit requirements. They are also recommended for anyone who wants to beautify their property and improve the environment. If additional capacity for storage of sump pump discharge is needed please consider the integration of a "dry well" with your rain garden project. Dry wells can be constructed within or underneath a rain garden and provide the required retention of water for projects within South Portland's combined sewer overflow areas. Click here to download the dry well design guidance PDF.

See other Drainage Plan options here.

Basic Features

Rain gardens are attractive and functional landscaped areas that are designed to capture and filter runoff from roofs, driveways, and other hard surfaces. They collect water in bowl-shaped, vegetated areas, and allow it to slowly soak into the ground.

Site Suitability

Rain gardens can be designed for all soil types. Soil permeability should be tested to aid in design. As rain gardens are designed to drain, the rain garden surface should be above the seasonal high groundwater table.

Rain gardens vary in size, but are typically 20-30% of the drainage area to be treated. A rain garden for a single-family home is typically between 150 to 300 square feet in size. Rain gardens should be built 10' away from existing structures.

Design and Installation

Many home or business owners can install a rain garden themselves, usually with ordinary lawn and garden tools. Many landscaping professionals are familiar with the rain garden concept and can help with design and installation.

Download detailed design specifications for Rain Gardens.


Watering is important during the first growing season while the plants are becoming established. As the garden matures, some of the perennials may need to be divided if plantings become too crowded. Typical landscaping maintenance is needed thereafter, such as replacing mulch and weeding.