A garden pond, fountain or similar water feature can be an attractive landscaping element in your backyard. Various types of plants may be grown in such a water feature, including fragrant water lilies and ornamental grasses. Sometimes, these plants--or foreign plants, such as moss or algae--may need to be eradicated because they are getting out of control. Backyard gardeners and homeowners can kill water plants in a variety of ways, depending on their needs.
Apply potassium permanganate--a natural oxidizer--to kill moss or algae. Algae and moss are some of the most common types of aquatic plants that become nuisances. If you have a small water feature, add 0.04 grams of potassium permanganate for every 5 gallons of water. Use a gram scale, or a measuring spoon; 1 tsp. of potassium permanganate holds approximately 7 grams of the product.
Calculate your garden pond's acre-feet measurement if you need to kill algae or moss in a large pond. Multiply the pond's depth by its surface acres. For example, a half-acre pond with a depth of 5 feet has an acre-feet measurement of 2.5. Multiply the acre-feet by 5.4. The resulting number is the amount of potassium permanganate, in pounds, that you must pour into the pond.
Spray the water plants with an aquatic herbicide formulated with glyphosate, a systemic chemical that kills all types of aquatic vegetation. This method is best for plants on the water's surface or on the edge of your water feature, such as lilies or marsh grasses. Example products include Rodeo and AquaMaster. Mist all exposed portions of the plant with the herbicide.
Treat your water feature or garden pond with a granular aquatic herbicide formulated with 2,4-D. This approach is ideal for submerged water plants, and includse products like AquaKleen or Sonar. Sprinkle the herbicide granules into your water feature according to the product guidelines, as toxicity strength ranges by manufacturer. The granules will dissolve and kill all underwater plants.
Kill the water plants manually. This approach is best for small plant growths that aren't very widespread. Collect the plants using a scoop net or rake. If the plants are in the middle of a deep pond, you may need to use a boat or wading pants. Dry the plants in the sun to kill them, then discard or place in your compost bin.