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For The Garden

Invasive Pond Plants

Author: Cathy Cromell
Issue: July, 2014, Page 106
Floating water hyacinth



Avoid these aggressive growers for a healthy eco-system

Water gardens are full of wonderful surprises, including the discovery of how quickly most aquatic plants actually grow—and grow and grow. They multiply so rapidly, in fact, that if left unchecked, their foliage can cover the pond’s surface in no time.

Although such abundant lush greenery appears enticing, it may produce unintended consequences. Open water is essential to promote air and water circulation for a naturally sustainable pond ecosystem, so allowing floating plants to cover no more than 50 to 70 percent of your pond’s surface is key.

Disadvantages
Aquatic plants’ ability to spread aggressively has consequences that reach beyond a water garden’s perimeter. Their seeds or bits of reproductive plant material “travel,” hitching a ride with birds, wildlife, wind, flood waters, the soles of shoes, or tires on bikes and autos. Deposited in or near streams, rivers, lakes, wetlands, canals, golf course ponds and irrigation ditches, these non-native plants begin to reproduce and spread.

Invasive aquatic plants form dense mats of vegetation, blocking sunlight from native flora beneath the water’s surface. This inhibits photosynthesis and reduces dissolved oxygen in the water. As a result, native plants die, eliminating food for fish and other wildlife. As abundant plant matter decomposes, oxygen is consumed without sufficient replacement. The water becomes murky and unfit as a wildlife habitat. Recreational opportunities are lost, and millions of dollars may be spent to keep such essential waterways as rivers or agricultural canals open.
Parrot feather


Plants To Avoid
Five aquatic species are described in Invasive Non-Native Plants That Threaten Wildlands in Arizona (swvma.org/InvasiveNon-NativePlantsThatThreatenWildlandsInArizona.pdf). Two of these species are commonly used in water gardens:

Floating water hyacinth (Eichhornia crassipes)—This plant is on Arizona’s prohibited, regulated and restricted noxious weed list. Also avoid anchored water hyacinth (E. azurea).

Parrot feather (Myriophyllum aquaticum)—In the same genus as Eurasian watermilfoil (M. spicatum), this highly invasive species has been known to clog bodies of water in the East and Midwest.

Other popular pond plants have invasive characteristics. For example, papyrus (Cyperus papyrus, C. involucratus, C. prolifer) “escaped” their original water gardens in at least eight states, including Arizona, to establish along canal banks or in wetlands with regular moisture. Floating water primrose (Ludwigia peploides), hydrilla (H. verticillata), swamp morning glory (Ipomoea aquatica) and water lettuce (Pistia stratiotes) appear on varied regulatory noxious weed lists.
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