To know how well your soil is draining, you’ll need to test the permeability of your soil. Ideal soil holds a balanced amount of water and air. Testing for permeability, also called the percolation test, can determine whether organic material, such as compost or manure, should be added to improve your garden bed soil condition. Although the process for fixing problems with permeability is roughly the same no matter if your soil drains too fast or slow, the goal is to get your soil to drain properly and make it ready for planting.
Dig a hole in your garden area that has been thoroughly dry for three to four days. The hole should be 2 feet wide by 18 inches deep. Stand a yardstick or tape measure up in the center of your hole and hold it there, or have a friend hold it for you.
Fill the hole with water all the way to the top. As you start to add water, expect it to begin to drain right away. A dense soil will drain slowly, while a loose soil will drain quickly.
Start a stopwatch or note the time on your wristwatch as soon as the hole is full, and observe the height of the waterline on the ruler. Allow the hole to drain for exactly an hour and note the drop in the water’s height from start to finish along the ruler. The ideal drainage rate is one to two inches in one hour.
Slow down the drainage of a sandy soil if the water runs faster than 1 to 2 inches an hour by filling in the hole and adding 4 to 6 inches of compost, well-rotted manure or humus over the entire garden bed. Turn the soil to mix the organic material in well.
Speed up the drainage of a clay soil if you find it takes longer than an hour to drain 1 to 2 inches of water. Spread 2 to 4 inches of compost over the bed, followed by the appropriate amount of garden gypsum based on manufacturer's instructions. Thoroughly mix the compost and gypsum in with the existing soil.
Repeat testing the permeability again after a few more dry days. You can continue to add organic matter to your bed and recheck the drainage as often as needed until you find it is draining at the right rate.