Once you've decided where to place your garden, you'll want to scoop out a bowl-shaped depression. The center of the depression should be approximately six inches deep and the sides of the garden should slope gradually to the middle. The dug-up dirt should be used to bolster the lowest side of the garden to ensure that water does not trickle out. Add stones, logs or other ornamental features to break up and spread out the flow of water.
Once that is done, you are ready to start planting. Choose hardy native plants for your rain garden.... Water the plants in your rain garden every other day until they are established. They won't need any further watering. Once the plants are grown, add wood mulch to your garden to increase absorbency and control weeds.
Make sure your plants don't get covered by sediment move or replace plants that aren’t thriving."