By Debbie Brown, PC EMG
Rain gardens are often misunderstood. They are envisioned as constantly wet spaces suitable for only plants tolerant of growing in a mud puddle and therefore a prime breeding area for mosquitoes. Thankfully that is not the case. Instead, rain gardens are specifically designed to be filled with plants requiring varying levels of moisture. They are beautiful and multi-functioning gardens which greatly benefit our property and community.
The primary purpose of a rain garden is to temporarily hold runoff from impervious surfaces such as roads, driveways and rooftops. The runoff from heavy rains is absorbed by the plants or infiltrated into the ground. This storm water management practice improves water quality by reducing the amount and speed of runoff and by filtering out pollutants. A rain garden allows about 30% more water to soak into the ground than a conventional patch of lawn. Acting like a sponge, they keep excess floodwaters from running into the streets, yards, and basements. These garden spaces are highly attractive habitats for birds, butterflies, and other pollinators.
Placement of a rain garden can be anywhere along the natural runoff pathway, typically in the downward slope of a property. If necessary, runoff can be directed into the garden through pipes or swales. Keeping at least 10 feet away from building foundations, avoiding steep slopes and underground utilities or a septic field, placement should be where the water table is high and rain will easily absorb into the soil. Once water collects in the rain garden, infiltration may take up to 48 hours after a major rainfall. Mosquitoes aren’t a concern since they generally need 10-14 days to develop in standing water.
Rain gardens should cover an area about 20% the size of the roof, patio, or pavement draining into it. The typical size for a residential home is between 100-400 square feet. Their finished depth should be 6-8 inches lower than the surrounding surface. They are shaped longer than they are wide and arranged perpendicular to the slope of the land in order to catch the maximum amount of rainfall.
When choosing plants for a rain garden, include a mix of groundcovers, perennials, shrubs and even trees (if the garden is large) because different plants filter pollutants differently. Choose native or non-invasive plants that are adapted to the local environment. Natives are always the best choice since they are low maintenance, pollinator friendly and establish deep roots. Consider those that have ornamental value, such as flowers, berries, unique leaves or bark for interest all year.
Virginia Cooperative Extension Publication 426-043 lists dozens of possibilities. They include the ground covers: Green-and-Gold and Foamflower. Grasses: Sedges and Switchgrass. Ferns: Christmas and Cinnamon. Perennials: Asters, Beebalm, Blackeyed Susan, Goldenrod, Columbine, and Joe-Pye Weed. Shrubs: American Beautyberry, Oakleaf Hydrangea, Spicebush, and Chokeberry. Trees: Eastern Redbud, Serviceberry, and Fringetree.
There are three distinct zones to be considered when planting in the rain garden. Zone 1 is located in the center of the bed and requires plants that can tolerate wetter conditions, such as Swamp Milkweed and Mountain Mint. Zone 2 surrounds zone 1 and calls for plants that can tolerate occasional standing water, for example, Wild Blue Phlox, Mistflower, and Bergamot. Finally, zone 3 is located on the outer edge of the garden and is most suitable for plants that prefer drier conditions, like Blue False Indigo, Coneflowers and Wild Petunias.
Once established, rain gardens are low maintenance. They simply need to be monitored for debris that could clog the garden and prevent it from functioning properly. Periodically check after a rainfall to make sure water is not standing in the garden for more than four days. If it is, aeration with a pitchfork may be necessary to improve infiltration. Weed as needed. After an initial 2-3 inch layer of mulch, refrain from adding mulch each year as it will fill in the garden so it no longer holds water or functions properly.
Homeowners who voluntarily establish a rain garden are making a personal contribution to clean water in their community and benefiting their property. Patrick County Master Gardeners will be available at the Stuart Farmer’s Market on June 25th with more information on rain gardens and also composting. PCMG will provide a program on composting at WHEO 92.7 on June 22.
