How to Build a Rain Garden

Although a low-lying area might seem like a natural for a rain garden, you need a place that isn't overly soggy already. Stay at least 10 feet from the house and at least 50 feet from a septic system or slopes greater than 15 percent. Call 811 to make sure underground utilities aren't in the way. Once you have a tentative site, test the soil's percolation rate. Dig a hole 2 feet deep and time how long it takes for 8 to 12 inches of water to disappear. For example, if 8 inches drains in 12 hours, the rate is 8 inches divided by 12 hours, or 0.67 inches per hour. A rate higher than 0.5 is great—your rain garden needs to be just 18 inches deep. If the rate is lower than 0.5 you'll have to dig 30 inches deep. If the percolation rate is less than 0.1, the site isn't suitable for a rain garden.