A Rain Garden at Your Downspout
by Heather McCargo
The Northeast continues to experience torrential rains with increasing frequency as the climate crisis intensifies. While we organize for large-scale systemic solutions to the problems we face, we can work locally, in our own neighborhoods, to mitigate the impacts of these shifting weather patterns.
Forests and meadows are able to absorb massive amounts of rainfall, slowing the water’s path into streams and rivers, filtering out pollutants, recharging groundwater, cleaning our air, and moderating temperatures.
Our cities and suburbs are much less absorbent due to impermeable surfaces and minimal vegetation. Many municipalities treat rainwater as a waste product, where it is quickly diverted into culverts and underground pipes. This tightly channeled water, tainted with pollutants, eventually discharges into natural streams with explosive force. Heavy rain can overwhelm municipal systems, mixing rainwater with sewage and causing human waste to flow into streams and coastlines.
We can change this, and it can start at your downspout.
Planting wetland plants that thrive in intermittently wet soils can create a beautiful garden that will attract butterflies, bees, birds, and amphibians while directing rainwater back into the earth rather than diverted as waste.
Rain garden species, from left to right: golden groundsel, Joe-Pye weed, winterberry, blue lobelia, cardinal-flower, witch-hazel, swamp milkweed, blue vervain
How to create a downspout garden:
At the outlet of your home’s downspout, create a water catchment area by digging a hole 18” wide by 12” deep and fill it with 1-2” stones. This will dissipate the force of water as it is funneled down the spout and allow for an easy entry into the soil. The area surrounding the gravel hole can be slightly depressed by 1” to expand the area that holds the water. Once this area is planted the gravel will not be visible. Large rain gardens are sometime more deeply recessed, but in a small space a more subtle depression looks better and still can handle a lot of runoff.
If lawn is growing at the site of your water catchment area, first remove the sod and roots from the area to be planted. You can dig it out with a fork, or you can sheet mulch. Sheet mulching is easier, but takes more time. Once you have removed the grass, a good natural compost or undyed bark mulch will restore the microbial community to the soil and provide all the nutrients needed by resilient native species. If the soil is heavily compacted (e.g., by heavy construction equipment or foot traffic), then you should loosen the top foot of soil with a digging fork before adding the mulch.
After you have prepared the water catchment area and the space to be planted, flood it with a hose or watch it during a heavy rain to see if the grade needs to be adjusted. This will also give you a chance to see where it spills over. If the bed is near a sidewalk or driveway, you may want to edge it with a lip of brick, stone, or wood, which helps hold the moisture and mulch in place.
Determine the amount of sun site receives by watching it throughout the day, so you can choose the right plants. Measure the size of area you are planting to determine how many plants you will need. Plant densely— the plant stems, foliage, and their root systems absorb and hold the extra water. Site the woody plants first, then add the perennial species. In general, the taller plants go in the back or mid section of the planting, with lower ones in front.
Suggested Native Plants for Rain Gardens
Part or full sun
Common buttonbush Cephalanthus occidentalis 5’ (tall) x 5’ (spacing width)
Common winterberry Ilex verticillata 4-7′ x 5′
Rosy meadowsweet Spiraea tomentosa 3′ x 3′
Pussy willow Salix discolor 10′ x 5′
Smooth arrowwood Viburnum dentatum 7′ x 5′
Swamp milkweed Asclepias incarnata 3′ x 2′
Asters Symphotrichumspacenovae-angliae, S. novi belgii 3′ x 2′
Marsh-marigold Caltha palustris 18″ x 16″
Joe-Pye weed Eutrochium maculatum 5′-7′ x 3′
Boneset Eupatorium perfoliatum 3′ x 2′
Meadow bottle gentian Gentiana clausa 1′ x 16″
Blue iris Iris versicolor 2′ x 18″
Cardinal-flower Lobelia cardinalis 3′ x 18″
Golden grounsel Packera aurea 1′ x 1′
Three-lobed coneflower Rudbeckia triloba 4′ x 2′
Blue vervain Verbena hastata 5′ x 2′
Shade
Coastal sweet-pepperbush Clethra alnifolia 5′ x 4′ (height x spacing width)
Witch-hazel Hamamelis virginiana 8′ x 3′
Northern spicebush Lindera benzoin 10′ x 3′
Highbush blueberry Vaccinium corymbosum 5′ x 3′
Cinnamon fern Osmundastrum cinnamomeum 3′ x 2′
Royal fern Osmunda regalis 3′ x 2′
Cardinal flower Lobelia cardinalis 3′ x 18″
Blue lobelia Lobelia siphilitica 18″ x 18″
Golden groundsel Packera aurea 1′ x 1′
For more information on rain gardens, check out:
Rain Gardens: Sustainable Landscaping for a Beautiful Yard and a Healthy World by Lynn M. Steiner and Robert W. Domm