Rain Gardens – A Solution for Runoff

by | Jul 5, 2017 | Flood, Flooding, Garden Design, Native plants, Stormwater

This rain garden used stone for a berm and muhly grass as a decorative and functional plant. Photo credit, Jerry Patee

Tropical Storm Cindy’s early arrival soaked northwest Florida this month, followed by even more heavy rain. Homes in low areas and along the rivers flooded and suffered extensive damage. That being said, we are just entering our summer “rainy season,” so it may be wise to spend extra time thinking about adjusting your landscape to handle our typically heavy annual rainfall.

For example, if you have an area in your yard where water always runs after a storm (even a mild one) and washes out your property, you may want to consider a rain garden for that spot. Rain gardens are designed to temporarily hold rainwater and allow it to soak into the ground. However, they are quite different aesthetically from stormwater ponds, because they are planted with water-tolerant trees, shrubs, groundcovers and flowers to provide an attractive alternative to the eroding gully that once inhabited the area! Rain gardens are not “created wetlands,” but landscaped beds that can handle both wet and drier conditions. Many of the plants best suited for rain gardens are also attractive to wildlife, adding another element of beauty to the landscape.

A perfect spot for a rain garden might be downhill from a rain gutter, an area notorious for excess water and erosion. To build a rain garden, the rainwater leaving a particular part of the property (or rooftop), is directed into a gently sloping, 4”-8” deep depression in the ground, the back and sides of which are supported by a berm of earth. The rain garden serves as a catch basin for the water and is usually shaped like a semi-circle. The width of the rain garden depends on the slope and particular site conditions in each yard. Within the area, native plants are placed into loose, sandy soil and mulched.   Care should be taken to prevent the garden from having a very deep end where water pools, rather allowing water to spread evenly throughout the basin.

This larger rain garden, or bioretention area, functions as stormwater treatment for a large parking lot in North Carolina. Photo credit: Carrie Stevenson, UF / IFAS Extension

Besides reducing a problematic area of the lawn, a rain garden can play an important role in improving water quality. With increasing populations come more pavement, roads, and rooftops, which do almost nothing to absorb or treat stormwater, contributing to the problem. Vegetation and soil do a much better job at handling stormwater. Excess sediment, which can fill in streams and bays, and chemicals from fertilizers and pesticides are just some of the pollutants treated within a rain garden via the natural growth processes of the plants.

A handful of well-known plants that work great in rain gardens include: Louisiana iris, cinnamon fern, buttonbush, Virginia willow, black-eyed Susan, swamp lily, tulip poplar, oakleaf hydrangea, wax myrtle, Florida azalea, river birch, holly, and Southern magnolia. For a complete list of rain garden plants appropriate for our area, visit the “Rain Garden” section of Tallahassee’s “Think about Personal Pollution” website.

For design specifications on building a rain garden, visit the UF Green Building site or contact your local UF IFAS County Extension office.

Carrie Stevenson
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