Preservation of Rivers and Ponds

Using Plants to keep a Pond Clean

B Warade
Started by B Warade on
16 Nov 2014 at 23:12
Associate, Water consultant
Know-how: Water

Plants are more than just a beautiful addition to a backyard pond. They also serve an important function in maintaining an appropriate balance of nutrients in the pond’s water. Plants not only reduce the amount of algae that is able to grow, but also use waste materials from fish, providing a natural water filtration mechanism. Choosing the right combination of aquatic plants from the four categories will help keep your pond water clean and clear without the addition of chemicals.

Submerged Plants

1) Select plants that grow below the surface of the water. Submerged plants have the largest contribution to water quality. They function as oxygenators during daylight hours, providing oxygen for fish, and they supply fish with excellent cover. Submerged plants compete with algae for use of nitrogen produced from fish waste and decaying plant material. Examples of submerged plants are hornwort (Ceratophyllum demersum), hardy in U.S. Department of Agriculture plant hardiness zones 5 through10; jungle val (Vallisneria americana), hardy in USDA zones 4 through 10; and cabomba (Cabomba caroliniana), growing in USDA zones 6 through 10.

2) Pot submerged plants in small containers filled with gravel. The roots of these plants anchor the plant in place, but do not function in nutrient uptake. Potting of these plants allows for easy removal for thinning or winterization.

3) Thin or remove submerged plants as needed to prevent overgrowth within the pond.

Floating and Surface Plants

1) Pick plant species that grow flowers and leaves on the surface of the water. The difference between floating and surface plants is that floating plants float freely on the water’s surface without attached roots, while surface plants have roots that extend down and anchor into the pond’s soil.

2) Maintain surface area coverage by floating and surface plants at approximately two-thirds coverage. These plants provide shade for fish and limit the amount of UV light required for algae to grow. Examples of floating plants include duckweed (Lemna minor), USDA zones 6 through10; sensitive plant (Mimosa pudica), USDA zones 9 through11; and water lettuce (Pistia stratiotes), USDA zones 9 through 10. Examples of surface plants are water hawthorne (Aponogeton distachyos), USDA zones 6 through 9; variegated four-leaf water clover (Marsilea mutica), USDA zones 5 through10; and water lotus (Nelumbo lutea), USDA zones 4 through 10.

3) Remove plants if coverage exceeds two-thirds of the pond's surface area. Too much coverage can inhibit the photosynthesis activities of the submerged, oxygenating plants.

Marginal Plants

1) Choose plants that grow well in constantly moist or soggy soils or that grow well in standing water. A few examples of marginal plants are western blue flag iris (Iris missouriensis), USDA zones 3 through 8; sweet flag (Acorus calamus), USDA zones 7 through 10; and dwarf bamboo (Sasa pygmaea), growing in USDA zones 6 through10.

2) Plant marginal plants along the outer edge of your pond. The roots of these plants attach to the muddy soil and the foliage grows above the pond’s surface. These plants compete with algae for available nitrogen in the water.

3) Avoid selecting marginal plants that spread rapidly or are invasive, such as cattails.

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Iouri Vaisman
Just to warn that the " 2/3 of the area" rule for the floating plants should be taken with a bit of caution as it depends on a few factors such as the depth of the pond, weather conditions etc. In the hot climate areas in AUS we typically not use permanent/floating plants more than 1/5 - 1/4 of the area, especially in the shallow ponds. With 2/3 of the pond covered by the weeds (either permanent or floating) - I would call such a pond - a wetland. Happy to be corrected on this. Regards, Iouri
Carol Liu
Great tips.
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