Rain gardens have become a hot trend locally and across the country. The theory behind rain gardens is they catch the runoff from your property, allowing it to soak into the soil. This reduces runoff, trapping harmful pollutants and the amount of water leaving the property. While the idea and design of a rain garden is good, there seem to be some misconceptions about them.
A rain garden is a depression that allows rain water to soak into the soil. The purpose of a successful rain garden is to trap and hold water, allowing it to gently soak into the soil within 24 hours. I get questions that usually start with the statement, “I have a wet spot, and I thought a rain garden would help absorb the extra water. Do you have any recommendation for building and plants?”
A rain garden is not designed to fix already existing water issues. A rain garden will make this situation worse. Most often, moisture or drainage issues do not have a simple, low-budget fix. Solving water movement issues requires planning and solutions that really solve the problem, not just passing it along to your neighbor downhill.
Correctly constructed rain gardens should be located on a gentle downward slope and at least 10 feet or more from the house. This prevents foundation problems.
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The bowl or depression should be at least 4 to 8 inches deep or more. It can be dammed up on the low side and gently sloping around the edges to the surrounding grade. Size is also important. Somewhere around 100 to 300 square feet is an ideal size for an average roofline downspout. Keep in mind a rain garden is not designed to trap all rainfall, just the first inch or so.
To work properly, there needs to be good infiltration so the water soaks in rapidly, not becoming a mosquito incubator. Loosen up the base several inches deep and incorporate organic matter into our heavy clay soils to improve the drainage.
The last point I want to emphasize is the word “garden.” A rain garden is a garden where plants grow. It requires continued maintenance. It is not a plant-it-and-forget-it project. This is often the second misconception I get when discussing rain gardens.
A certain amount of work is required. Yearly maintenance includes spring cleanup, weeding, controlling invasive plants and, yes, potentially watering during dry periods. Native plants are most often mentioned as the ideal type of plants to utilize in a rain garden as they are better adapted and deeper rooted. But also keep in mind a plant that likes wet soils will probably suffer during prolonged dry periods.
Rain gardens are a great way to help control water movement and improve our local water quality. But think through the concept of a rain garden and make sure you understand its purpose and construction. This is the only way to truly have success and not create a maintenance nightmare in your backyard.