Why you need a rain garden (even in a drought)
With scant rain and temperatures in the 90s, this does not seem like the year to talk about rain gardens. Yet storms that drop large volumes of rain onto dry, compacted soil, however infrequent, create excess runoff and are responsible for flash flooding.
In recent years, Western Pennsylvania has been inundated with damaging rains. The answer for homeowners might be installing a rain garden, a practical and beautiful way to manage storm water runoff.
A rain garden is strategically placed to collect storm water and allow it to soak into the soil. At homes, most runoff comes from the roof and the driveway. Just 1 inch of rain on a 1,000-square-foot roof yields 623 gallons of water, according to the Penn State Cooperative Extension Service.
Here are some tips for siting a rain garden:
• Chose a spot at least 10 feet away from your house or your neighbor to avoid creating moisture problems in the house or basement.
• Avoid areas where water ponds. A rain garden should filter the water so it infiltrates the soil and recharges groundwater aquifers.
• Do not place a rain garden over a septic system, drinking water well or at the base of a tree.
• Perform a drainage test by digging a hole 18 inches deep, filling it with water and allowing it to drain. Refill with water and check the filtration rate with a ruler. If the hole drains at a rate of a half inch per hour, it will work as a rain garden.
Plants for a rain garden must be able to tolerate dry spells between rain events. They must be adaptable over three zones: Zone 1, the lowest area, will hold the most water, and plants there must be able to survive in up to 6 inches of water for a couple of days. Zone 2, the middle zone, drains more quickly, but plants still need to tolerate a few inches of water. Zone 3 is the transition zone between the rain garden and rest of the garden. It is flooded infrequently, during very heavy rains.
The Penn State Master Gardeners of Allegheny County maintain a rain garden in North Park. Nestled behind Shaler Grove, off East Ingomar Road, the rain garden was created six years ago to catch runoff from the road, driveway and hillside and filter storm water before it enters the groundwater and, later, North Park Lake.
The North Park garden contains many native plants, including blue flag iris (Iris versicolor) and Pennsylvania sedge (Carex
pensylvanica), both zone 1 plants.
Button bush (Cephalanthus occidentalis), a shrub with spherical white flowers favored by butterflies, and blue star (Amsonia) are featured zone 2 plants. The transitional zone 3 has wing stem (Verbesina alternifolia), which sports yellow blooms from August through October, when most gardens are starting to look tired.
Some other plants in North Park’s rain garden:
Zone 1: black willow (Salix nigra), river birch (Betula nigra), sycamore (Platanus occidentalis), switch Grass (Panicum virgatum).
Zone 2 (some also Zone 3):
Eastern redbud (Cercis canadensis), sweetspire (Itea virginica), ‘Raspberry Wine’ bee balm (Monarda), mountain mint (Pycnanthemum
muticum), New York ironweed (Vernonia noveboracensis).
Zone 3: gray dogwood (Cornus racemosa), ‘Orchid Frost’ spotted dead nettle (Lamium), ‘Solanna Golden
Sphere’ tickseed (Coreopsis).
Make a visit to North Park to get ideas on how to incorporate these plants and a rain garden into your landscape.
Denise Grabner is a Penn State Master Gardener, a volunteer program that supports the outreach mission of Penn State Extension. Have a gardening question? Email it, along with photos, to the Garden Hotline, staffed by the Penn State Extension Master Gardeners of Allegheny County at alleghenymg@psu.edu. They are answering emails from home during the pandemic but unfortunately cannot take phone calls or office visits at this time.