Rain gardens are specially designed to gather and absorb runoff water from rainstorms to reduce the amount of pollutants that enter our waterways. Contrary to a water garden or pond, a rain garden is often dry. Water that collects in a properly designed rain garden typically drains within a day or two. Rain gardens can be an attractive, functional and environmentally conscious landscape solution.
Rain gardens reduce runoff, absorbing up to 30% more rain water than a traditional lawn or landscape. The soil and vegetation in rain gardens provide filtration removing upward of 80% of the pollutants accumulated in the runoff from roofs and roads. To achieve the most functional rain garden, consideration should be made for the location, soil structure, plant selection and maintenance.
Rain gardens should be situated in an area where rain water gathers; however the site surroundings are important. The garden should not be a space closer than 10 feet to a house or other building. It’s best to avoid planting a rain garden on a steep slope or an area where water flows quickly and heavily. The runoff should accumulate slowly to allow absorption and avoid erosion. Identify the impermeable surfaces on your property, such as a driveway, sidewalk or rooftop, where water is draining into the landscape. Observe the flow of water during a rain storm and identify locations where a rain garden could collect this water.
Determine the soil composition by performing a soil test through your local extension agent. Soil with heavy clay or sand will need more amending than soil with good absorption rates. Remove the top 6-8 inches of soil from the area where your rain garden will be located to create a flat-bottom depression with gently sloped sides. Amend the remaining soil with the appropriate ratio of compost and topsoil based on what was discovered from the soil test. Till the amendments into the rain garden soil. After planting, a 3-inch layer of mulch can be placed over the soil bringing the garden surface slightly below the existing landscape surface.
Native plants are typically best suited for a rain garden. Their root systems are able to absorb the nutrients and water in the soil and can better withstand the weather extremes. Natives don’t require supplements and can attract butterflies and bees. Perennials, shrubs and wildflowers can be good candidates, but always avoid using invasive species. Plants with greater tolerance for moisture should be placed in the lower lying areas of a rain garden. To increase visibility, position taller growing species in the center with lower species toward the outer borders.
As with any garden, weeding is necessary especially during the first two years. Mulch can help inhibit weed growth and once the rain garden plants fill in, the weeds will likely be crowded out and minimized. Supplemental watering should only be necessary during dry spells of the first year of the garden, if appropriate rain garden plants were selected. After this, the rainfall amount should be sufficient to sustain the garden.
There are many detailed guides that offer instructions for establishing a rain garden. You can also work directly with a professional landscaper to incorporate a rain garden into your overall landscape design. The rain garden can be as simple or grand as you want but it does not need to be overcomplicated. It is quite simply a beautiful solution to an environmental problem.
Cynthia Domenghini is an instructor and coordinator for K-State’s horticultural therapy online certificate program.