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September 29, 2015

MADISON -- Bag it, seal it, take it out with the trash.

That's the best way to dispose of a nonnative plant if you need to clean out your water garden before colder weather sets in, Wisconsin Department of Natural Resources experts say. Water garden plants are often discovered in Wisconsin waters this time of year when pond owners reduce plant numbers or drain ponds before winter.

The problem is that nonnative aquatic plants can quickly spread, harming fish and wildlife habitat as well as limiting recreation, said Susan Graham, a DNR lakes biologist. A recent case in point involved water lettuce , a prohibited invasive species - that was discovered in Lake Mendota in late July.

Water lettuce.
Individual water lettuce plants can form dense mats.
Photo Credit: WDNR

Water lettuce is a floating aquatic plant that quickly reproduces and can reach densities that choke out other plants and inhibit recreational activity. It is illegal to sell or possess any prohibited species due to the potentially large negative economic or environmental impact. The discovery of water lettuce in Lake Mendota triggered a response effort throughout August by local DNR staff to locate and remove the plants.

Water lettuce reproduces rapidly.
Water lettuce reproduces rapidly.
Photo Credit: WDNR

"Monitoring efforts found that the water lettuce was limited to the south shore of Lake Mendota near the University of Wisconsin-Madison campus," Graham said. "Staff and volunteers from several partner groups removed all of the water lettuce that could be found and this should prevent it from becoming a nuisance this year and hopefully into the future. The team's quick response prevented water lettuce from spreading throughout the lake."

Although water lettuce isn't thought to be able to survive a Wisconsin winter, discoveries of water lettuce in the Mississippi River in consecutive years suggest that seeds could overwinter. Additionally, its rapid growth means that it can reach nuisance densities in a single growing season.

Another common water garden species, water hyacinth, is also a recent addition to the prohibited invasive species list. It, too, has been discovered in Wisconsin waterways recently - at a public pond in La Crosse and in Arkdale Lake in central Wisconsin. In both instances, quick and organized responses from partner groups helped remove all of the plants before they could spread.

While avid gardeners frequently compost excess vegetation when preparing beds and water features for winter, prohibited species can spread if seeds or roots are carried away by birds, animals or heavy rains. Compost can also move invasive species when it is transported and used elsewhere. As a result, sealed plastic bags are recommended for disposal if you find a prohibited species in your garden.

To learn more, search the DNR website,, for "invasive species" or search here for a list of prohibited plants [PDF].

FOR MORE INFORMATION CONTACT: Bob Wakeman, DNR aquatic invasive species coordinator, 262-574-2149,; Susan Graham, DNR lakes biologist, 608-275-3329,; Jennifer Sereno, DNR Communications, 608-770-8084,

Last Revised: Tuesday, September 29, 2015

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