First, dig a hole about a foot deep. Fill with water and let it drain completely.
Immediately refill the hole and measure the depth of the water with a ruler. Fifteen minutes later, measure the drop in the water level in inches and multiply by four, to calculate how much water drains in an hour.
What is your soil's drainage rate?
If it drained between 1 and 6 inches per hour, then you have well-drained soil. If your rate was less than an inch per hour, your soil has poor drainage. If it drained more than six inches, your soil has excessive drainage.
What does this mean? What do I need to do?
If your soil has poor drainage there are a few things you can do. Amending the soil with compost or other organic matter will help with drainage as well as adding nutrients. You can also choose plants that tolerate wet conditions - there are many native plants that work well - hibiscus, bog lilies, pitcher plants, and many others.
Adding organic matter helps soil with excessive drainage as well. If the area gets a lot of sun, you may want to consider growing succulents. There are a number of aloes, agaves, yuccas and cactuses that are hardy in your area. Also, once established, native flowers like Rudbeckia and Echinacea can thrive in areas where drought-tolerant plants are needed.
With the right information, there's no need to let plants grow in a soil that's not right for them.