Though you can excavate a small (say, 5-by-10-foot) rain garden yourself, a landscaper with an earth-moving machine will get it done faster. Make sure machinery stays along the edge of the bed so it doesn’t compact the soil as it digs a wide depression about 2 feet deep with gently sloping sides. Mix in compost and sand, as needed, using the same proportions as for a swale. The end result should be a shallow basin with about 6 inches of “ponding depth,” or space for water to pool while it drains through 1 to 2 feet of amended soil.
Plant the center of the area with species that tolerate wet conditions, such as native sedges and lady fern. Around these, put plants suited to occasional standing water, like redtwig dogwood. At the furthermost edges go plants that prefer drier soil, such as native evergreen and deciduous shrubs.