By Jeff Rugg- Q: I have been thinking about putting in a rain garden. Do you have any advice on building one? What kind of plants can be planted in the flooded soil?
A: A rain garden is similar to other perennial flower beds you might build: It just holds water for longer. Rather than build a raised flower bed by adding organic matter to get better drainage, a rain garden is a flower bed built slightly lower so that water accumulates.
Rain gardens provide several benefits to your landscape. These gardens trap water, which will slowly soak into the soil. This helps your landscape because more water is available for a longer period of time, deeper underground. The water your plants don’t use will eventually reach the groundwater that, in many communities, supplies the wells that are slowly going dry.
Any water that doesn’t immediately wash into the storm drains reduces the amount of local flooding and shoreline erosion in retention ponds and rivers. In the long run, the water that has soaked into the ground also helps to keep an adequate flow of water in streams during droughts.
Shorelines, marshes, bogs, wetlands and swamps all have plants that tolerate or require water over its roots and will grow in a rain garden. Some like wetter soil, so plant them in the deeper central area.
Many rain garden plants grow best in full sun, but there are also many that will grow in shade. Choose rain garden plants that are the right height for your landscape. There are a variety of bloom times, color choices and flower fragrances.
Shoreline plants in nurseries may be labeled as “marginal plants.” A marginal is a plant growing on the margin between two habitats, such as pond and woodland habitats. Other shoreline plants may be labeled as “emergent plants.” An emergent plant has underwater roots, and it emerges above the water with the stems and leaves, such as a cattail. Moist prairie, mesic plants grow well in wet soil, so they will also work in a rain garden. Just like in the rest of the garden, some shoreline, marginal, emergent and mesic plants are annuals, and some are perennials.
Like any perennial flower bed, the plants will need to be watered if it doesn’t rain after they are planted. Once established, they won’t need to be watered very often. These hardy plants require less care and fertilizer than a lawn. As the plants bloom, they attract birds and butterflies.
The construction is easy. Measure the area the water will be coming from. If the water is coming from the roof gutters, measure how many square feet of roof area there is. If the rain garden is receiving water from a large, sloped, grassy area, measure the square footage of the lawn. The rain garden should be about one-third as big as the area that supplies the water.
Pick a low flat area in full sun that is not over a septic system and at least 10 feet from the house. Dig a level-bottomed hole from 2 to 6 inches deep, with sides that slope down to the flat bottom. A deeper water garden will hold more water for longer.
Channel the water to the rain garden with a downspout, polyvinyl chloride pipe or shallow trench. Depending on the lay of the land, it may be necessary to build rain gardens in both the front yard and back. In heavy rains, the rain garden may overflow, so make sure the water drains away from the house.
Mosquitoes should not be a problem, as the rain garden is not supposed to have visible water left standing in it for more than a few hours. Even if it rains every day or two, there should not be standing water long enough for mosquitoes to become adults. The eggs need to float in water for a week to hatch, so they will have dried out and died before then.
Email questions to Jeff Rugg at firstname.lastname@example.org.