Hughes Water Gardens Oxygenating Hornwort (1 Bunch - 6 Stem Plants) Excellent for improving water quality by providing oxygen and removing excess nutrients from pond water. Helps to control algae. Can be just dropped into the pond. Provides a screen of foliage at bottom of pond to help fish hide from predators. Very cold-hardy, overwinters on pond bottom. Vigorous grower. Easy to propagate. We recommend 1-2 bunches per square foot of pond surface area.