Building a Rain Garden in 10 Simple Steps

Building a rain garden can be complex or simple. We strive for simplicity here and an end result that’s both attractive and functional.

Rain gardens, formerly called bioswales or even just swales, are manufactured shallow depressions in your landscape that are designed to slow down the water running off roofs and pavement and allow it to infiltrate the soil.

Rain gardens are especially important in areas with shallow soil or extensive pavement.

Building a rain garden can be complex or simple. We strive for simplicity here and an end result that’s both attractive and functional.

Step 1 – Identify the downspouts and natural drainage patterns to the street or greenbelt.

Step 2 – Determine the composition of the soil: sandy, loam, clay guck. Heavy clay soils that predominate eastern San Antonio and suburbs may not allow enough water to infiltrate and percolate through the soil before becoming a nuisance. The general rule is that all standing water must infiltrate the soil or leave a detention facility, large or small, within 72 hours. Conduct a simple percolation test. Dig a 12-inch by 12-inch by 6-inch hole in dry soil. Pour in one liter of water. It should be gone in 24 hours.

Step 3 – Outline the borders of the rain garden with marking paint or an old hose. Think teardrop or kidney shape. There are not very many rectangles or triangles in nature.

Step 4 – Calculate the size. A ½-inch rain on a 1,000-square-foot roof could produce more than 300 gallons. A 200-square-foot area that is six inches deep could hold about 750 gallons. Hey, that’s the exact size for the WaterSaver Landscape Coupon! (See what I did there?)

Step 5 – Call 811 to prevent digging accidents.

Step 6 – Dig shallow. One inch depth at the top and 4-8 inches at the bottom. Use the soil excavated along the edges and bottom of the structure.

Step 7 – Select plants for the bottom, sides and top. You’re not required to use the WaterSaver Landscape Coupon and its permitted plants, but it certainly does make the process easier. Bottom: frogfruit, inland seaoats, iris, liriopeLindheimer’s muhly grass, coastal muhly grass, snakeherb.

Sides: crinums, iris, liriope, Mexican honeysuckle, milkweed, mistflower, purple heartSalvia, shrimp plant.

Top: Barbados cherry, damianita, oregano, plumbagoSalvia, rosemary.

Step 8 – Shop. Again, you don’t have to use the WaterSaver Landscape Coupons, but it saves you time as you can find all your plants at one or two locations. Partner nurseries are listed HERE.

Step 9 – Plant on 12-18 inch centers.

Step 10 – Water 3 times a week for approximately 4-5 weeks, in the absence of rain.

Think about building a rain garden in your landscape to help limit storm water and encourage infiltration to help our aquifers. Beauty and stewardship can go hand and hand.

Picture of Mark Peterson
Mark Peterson
Mark A. Peterson was a conservation project coordinator for San Antonio Water System before retiring. With over 30 years of experience as an urban forester and arborist, Mark is probably the only person you know who actually prunes trees for fun. When not expounding on the benefits of trees and limited lawns, you're likely to find him hiking San Antonio's wilderness parks or expounding on the virtues of geography and history to his friends.
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