Compacted and clay soil can drain poorly and cause plants roots to sit too long in wet conditions. If you have heavy clay or compacted soil, either amend the soil to make it more porous or choose plants that can tolerate wet areas. Sandy soil can drain water away from plant roots too quickly. For sandy soil, amend the soil or choose plants that can tolerate dry and drought-like conditions.
To test the drainage of a planting site, dig a hole that is about a foot wide and a foot deep. Fill the hole with water and allow it to all drain out. Before the hole has time to dry, refill it with water again. This time, using a ruler, measure the drop in water every 15 minutes for an hour.
After an hour, if the soil has drained only an inch or less, this is an area with poor drainage.
If the soil has drained about one to six inches in the hour, the site is well draining.
If more than six inches of water was drained in the hour, your soil is draining too quickly.