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Rain gardens
Are there areas of your garden that never seem to dry out? If so, you have the perfect foundation for a rain garden (also known as a swale). Whichever term you use, you can transform soggy soil into a practical and beautiful part of the garden with as little effort as it takes to turn a phrase. The main function of a swale or rain garden is to divert and direct water runoff, particularly after heavy rains. This is why you’ll often see them at the edges of parking lots, sidewalks, or beneath gutters. Even if you’ve never noticed soggy spots on your property, you might benefit from a rain garden because the average home creates more than 10,000 gallons of rainwater runoff each year. Don’t believe it? Calculate how much rainwater runs off your roof each year by multiplying your roof's square footage by 623. Next, divide the product by 1,000, and multiply the result by the number of annual inches of rainfall in your location. If that seems like too much work, take my word for it. A rain garden will keep water from building up in one area of your property, while improving water quality, creating habitat for birds and butterflies, and providing aesthetic interest to the landscape. The rain garden creates a filter for runoff. The lowest point of the rain garden only needs to be about six inches below the level of the surrounding garden, but make sure it’s away from the foundation of the house or other buildings. Good rules of thumb include directing water away from buildings with a channel and situating low points in the middle of your rain garden for maximum drainage. One of the easiest strategies for building a rain garden is to remove any existing grass from the site and line it with gravel. Then, simply cover the gravel with compost and plant with appropriate plants (discussed below). The improved drainage will cause water to move through the area and get it back into the ground, instead of standing at the surface, attracting mosquitoes. Rain gardens can also be disguised as dry creek beds, using stones, river rocks, and either native or non-native plants and grasses. If you prefer this aesthetic, remove grass or sod, dig to the desired level, and line with gravel, as described above. However, instead of covering with compost, arrange stones and rocks on top of the gravel to form a dry creek bed that will filter the water. Add a few plants around the margins for interest. Rain garden plants can’t mind having their feet wet sometimes. The tricky thing is that most rain gardens dry out in the summer, so the plants you choose also must be hardy and adaptable. Native plants excel in this regard because they have evolved to function well in our particular weather patterns—rain in the winter, drought in the summer. Natives that would thrive in a semi-shady rain garden include sword fern, trillium, Oregon saxifrage, wild ginger, Pacific bleeding heart, Oregon grape, monkey flowers, lupine, stream bank violet, and yellow-eyed grass. The Portland area has many excellent examples of rain gardens. My favorite is at the Southwest corner of the Oregon Convention Center (N.E. 1st Avenue and N.E. Lloyd Blvd. in Northeast Portland). The Convention Center’s rain garden features towering basalt columns and wetland plants in a long channel that imitates a mountain stream. This multi-faceted rain garden filters water from a 5.5 acre roof, saving the Convention Center an estimated $15,000 annually on storm water bills. It is dazzling, but its huge scale will likely provide more inspiration than instruction. For a more modest example, drive a few blocks east to the Liberty Centre parking garage (corner of N.E. 7th and N.E. Oregon Streets). This simple rain garden uses gravel, rocks, and easy-care plants like sedge to divert run-off, and would be easy to replicate at home. * * * Linda Drach is a trained OSU Extension Service Master Gardener. Send gardening questions to her at lindadrach@comcast.net. |
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