It’s April and usually that means lots of rain. “April showers bring May flowers,” indeed. In an ideal world plant roots absorb water with nutrients that travel through the plant’s vascular system and trigger production of shoots, leaves and buds. Plant roots absorb much of the rain, and the soil – replete with organic matter and microorganisms – holds the rest of the moisture until it’s needed.
In the real world, especially where humans live, large rain events often produce more water than the plants or soil can hold. The rain hits buildings and paved (impervious) surfaces and compacted soil that lacks organic material. The water runs off those surfaces with nowhere good to go – commonly called “stormwater runoff.”
As the water runs off the hard surfaces or treated lawns it picks up pollutants including fertilizers, pathogens, road salts, oils, sediments, toxic contaminants, and other chemicals before entering storm drains or heading directly for our waterways.
Preventing large scale stormwater runoff and the resulting “non-point source pollution” (pollution that is not from a single source such as factory) is daunting. It calls for re-building infrastructure (all those overloaded pipes under Buffalo), re-framing urban and suburban architecture and landscape design, massive streamside and lakeside planting projects, and lifestyle changes. It’s expensive and overwhelming for individuals, municipalities and politicians.
I daresay much of our society lingers in a state of denial, as it’s less scary to bury our heads in the sand – even as the pollution runs by our heads. It is all most discouraging.
One thing homeowners and gardeners can do is to build rain gardens that help to manage stormwater runoff and decrease pollution. A rain garden is basically a shallow depression, planted with shrubs and perennials, that is positioned to collect stormwater runoff from roofs, driveways, parking lots, or lawns. The plants (ideally native) are chosen for their ability to absorb and thrive in areas that are sometimes saturated with water.
On a larger scale similar projects are called “bio-retention basins.” We have several good examples in Buffalo.
Some basic guidelines follow that can help you decide about location and size of your rain garden, and whether to make it yourself or hire a CNLP to do the work. For detailed instructions I recommend “Rain Gardens: A How-To Guide,” produced by the WNY Stormwater Coalition in collaboration with most of your villages or towns, many colleges, agencies, and environmental engineering firms.
It was also funded by New York State Soil & Water Conservation Committee; New York State Department of Environmental Conservation and the Erie County Water Quality Committee. Go to erie.gov to find the five-page booklet.
Where and how big to make a rain garden?
Around homes, most rain gardens are 100 to 300 square feet and twice as long as it is wide. The size could be just 50 square feet on a small urban lot. (City homeowners should check whether city ordinances restrict the project.) A sloping location is recommended, and the garden’s depth depends upon the slope: A 3- to 4-percent slope (preferred) would require only a 4-inch deep garden; 8- to 12-inch slope equals about 10-inch depth.
• Placement at least 10 feet from house.
• Away from gas or water lines, or sewer/septic tank proximity.
• Full or partial sun.
• Decent drainage: Test this by digging a hole 8 by 8 inches. Fill it with water. The water should decrease 1 inch per hour, or it is not an ideal location.
• Soil: should contain about 25 percent organic matter. (You probably need to add compost.)
• A berm (like a pond wall) should be placed along the lower edge of the rain garden, to capture and slow water runoff during heavy rainfall.
I have simplified these specifications so look further into the best plan for your situation. For instance, the ideal sized garden depends upon the “drainage area” the garden will serve, calculated by the square feet of your roof divided by the number of downspouts. Then a “size factor” is added, that depends upon the distance from the house.
A rain garden is still a garden, so the plant choices should reflect your taste and what is important to you. Ideally you’ll choose native plants with high wildlife and pollinator value. The WNY Stormwater Coalition Guide lists the following plants:
• Swamp milkweed, Little Blue Stem, Partridge Pea, Big Bluestem, Black Eyed Susan, Wild Senna, Wild Blue Lupine, Beard Tongue (Penstemon digitalis), Smooth Blue Aster (Aster laevis).
• Herbaceous plants (native) for partial shade: Joe-pye weed, Blue lobelia, Silky Wild Rye, Indian Grass, Ox Eye Sunflower, Wild Blue False Indigo.
• Trees and shrubs: Buttonbush (Cephalanthus occidentalis), Silky dogwood, Winterberry holly, American elderberry (Sambucus canadensis), Arrowwood (Viburnum dentatum).
Be sure to seek “species” plants (the original native plants rather than hybrids) whenever you can. Understand that not all these plants are easy to find, and sometimes your garden center or nursery staff cannot obtain them – but it’s good to ask.
Local native plant experts are collaborating to develop better WNY resources for these and other native plants. You can use many other native or non-native plants that also absorb water efficiently.
Whether you take on a rain garden project like an engineer, or you just dig a slightly depressed garden on the side of the house with the most runoff, this is a good thing. You’re recharging or recycling local groundwater, benefitting birds and butterflies, decreasing the likelihood of basement flooding, and discouraging mosquito populations by removing standing water.
It is also more important to do this now. Scientists predict that global climate change will increase the frequency of extreme rain events, that will in turn increase episodes of water runoff. Meanwhile our infrastructure, especially urban sewers and drain systems, is getting older and more difficult to repair or replace. Populations increase, and green space decreases.
This spring might just be the time for a rain garden in every yard.
* Read Sally Cunningham's column from last week.
Sally Cunningham is a garden writer, lecturer and consultant.