Biology Question #3899

Amie, a 14 year old female from West Harrison asks on June 9, 2007,

How do you get rid of duck weed in a pond?

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The answer

John Cross answered on June 9, 2007

To solve this problem in the easiest and most friendly way, you should change the ecological balance of your pond.  For a quick fix in a very small pond, the best approach is just to remove it.  It takes time and patience, and you will need to keep at it until it is all gone.  Scoop out as much as you can every day or so with a net or a rake and throw it in the compost.  Duckweeds die quickly as they dry.  For the long term you should eliminate the duckweed's source of food by lowering the nutrient supply in your pond. Duckweed thrives on products of rotting material at the bottom of the pond and excess fertilizer draining from lawns or farmers' fields.  Plant a strip of grass as a barrier around the pond to absorb fertilizer run-off.  Naturally, you won't want to fertilize the grass barrier.  If you can, clean out the black muck that has collected at the bottom of your pond.  Take these steps and you will gradually reduce the amount of duckweed.  Finally, you can introduce animals that eat duckweed. Put in some herbivorous fish (koy or grass carp, for instance), or ducks.  They love duckweed.  As a last resort there are chemicals (herbicides) that kill duckweed and other aquatic plants, but I would avoid using them since the other methods work well, and (unless your pond is very large) they are not that difficult to do.  Keep in mind that some of these chemicals are toxic to fish, and some are expensive.  More information about duckweed control can be found at The Charms of Duckweed. Also, here is a fact sheet on duckweed control from Ohio State University.

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