Answer: Rain gardens are plantings set in low areas where rain water runoff collects; the plants are specially selected because they can tolerate the periodically extra wet soil. (Sometimes these spots are specifically designed to serve this purpose, they may be called somthing like "retention areas".) Here is a web site all about rain gardens with lots of homeowner information. Although it is developed further north, most of the plants would grow in your area, too.
I hope this gives you lots of ideas!
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