What Is a Rain Garden?
When you create a rain garden, you situate your garden to use rainfall and runoff from gutters and storm drains. Planning a rain garden is water-wise and ecologically low impact — and produces a beautiful garden that provides a home to birds, and butterflies and other insects. Not only do you save water when you create a rain garden, its placement (in the path of runoff water) prevents erosion. In addition, the path the water takes through the soil improves the water’s quality.
Water from rainfall and snowmelt contains untreated pollutants like salt and oil and flows directly into storm drains, contaminating our water sources. Although you wouldn't want to drink this water, it's perfect for watering your garden. The soil and mulch that the water travels through in your garden act as a filtering system that breaks up contaminates.
There are two approaches to rain gardening, but in either case you want water to drain from the garden surface within four hours:
Underdrained: These gardens are useful when you have a high water table. They employ a water piping system to help water drain from your garden after a heavy rain.
Self-contained: You must choose plants with roots that can tolerate wet conditions and your planting medium should be porous to promote drainage because no drainage system is used.
When you look at a rain garden you can’t really tell that it is different from any other gardens. They can be formal gardens, cottage gardens, woodland gardens, or almost any other garden that strikes your fancy. But plants that have deep roots fare better and, as you might expect, native plants are always a good bet. Although annuals can be planted in rain gardens, they require much more care, and part of the allure of the rain garden is its low-maintenance nature.
Generally, you create your rain garden in a low-lying area that gets rainwater runoff. You can create one near your downspouts (but not too close to your house) or at the bottom of a slope in your yard. Dig your garden 4-8 inches deep. Depending on the type of plants you intend to grow (bog lovers, perhaps), go ahead and line the depression with plastic. You can use any sod you remove to build up the sides of your garden. Amend the soil with a good quality compost.