Before you toil, know your soil.

Most soils are categorized as sandy, silty, or clayey. Sandy soil—it feels gritty and coarse—drains the fastest, clayey soil—sticky and clumpy—the slowest. In Western Pennsylvania, most of the soils have high clay content. Rain gardens can still work in clayey soil, but they will need to be larger.

Here are a couple of simple tests you can do to find out which kind you have.

Dig a 12-inch hole where you're considering putting your rain garden, and fill the hole with water. Sandy soil will drain completely within two hours and silty can take up to 6. Clayey soil may take up to 12 hours to drain. If the water's still there 12 hours later, you will need to augment your soil or look for another place to dig.

Take a handful of dirt and add a few drops of water. After kneading the soil in your fingers, roll it into a ball. Crush it between your forefinger and thumb, squeezing it upward into a ribbon. Lay the ribbon over your forefinger until it breaks from its own weight. If the ribbon is more than an inch long before it breaks, and it feels more smooth than gritty, keep looking.

If all the possible locations for your rain garden feature clayey soil, you can create your own suitable soil with a trip to your local garden store or landscape supplier. A good mix for a rain garden is 50–60% sand, 30–40% loamy topsoil and 5–10% organic material from yard waste compost.