Adding plants to a pond enhances its beauty and also helps keep the water clean by controlling algae and providing oxygen for fish and other pond life. Some oxygenating plants, such as elodea (also known as anacharis), grow completely underwater and consume nutrients that would otherwise feed algae. Others, like water hyacinth, drift on the surface and provide shade that inhibits algae growth. Unless the pond has a natural-earth bottom where plants can root, they must be placed in pots. That makes for easy maintenance—just remember to take nonhardy plants in before winter so you're not scooping decomposed gunk out of the pond come spring.