You don’t have to take a soil sample to a plant lab to measure its drainage ability. Here is a simple measurement technique for testing when your soil isn't soggy: (1) Dig a hole 12 inches deep and wide with straight sides and a flat bottom for accurate measurement of absorption. (2) Poke a 12-inch ruler into the bottom 1 inch deep. (3) Fill the hole to the top with water and let it drain overnight so the soil won't be completely dry when you test. (4) The next day, fill the hole to the top with water again. (4) After one hour, check to see how much has drained. If the water just touches the top of the ruler, it has drained 1 inch. (5) Continue checking and recording the amount of decrease every hour until the hole is empty.
Good drainage averages about 2 inches per hour. If the water drops more slowly, the soil needs to be amended with gritty mineral matter and compost. Conversely, if it drops faster, you need to add extra organic matter to improve water retention.