How To Prevent & Eliminate Duckweed

Duckweed invades many garden ponds, here is our guide to understanding why it occurs and how it be eliminated or prevented.

Duckweed's botanical name is Lemna minuta. It can be a real nuisance and many people report that, once they've cleared their pond of green water and blanket weed, the next problem that arises is duckweed.

The reason for this is that, just like blanket weed and green water, duckweed feeds off the nutrients in the pond. So once the others are out of the way, it is free to feed and multiply with the result that it covers the pond.

During the summer duckweed can quickly multiply, especially in slow moving or still water. It has been known to double in quantity at times in one day.

What Does Duckweed Look Like?

It looks like hundreds of tiny leaves around 50mm in size similar to water cress. Duckweed usually appears in the spring and sinks to the bottom of the pond in the winter to return the following year.

Where Does Duckweed Come From?

Duckweed can be introduced into your pond by accident on plants you've bought or through animals and birds. This can be unavoidable but one of the easiest ways to try and stop duckweed from entering the pond on new plants is to isolate them for a couple of weeks before introducing them.

Can it Be Treated?

The best way to manage duckweed is by scraping the surface of your pond and collecting it in a net. Leave the duckweed on the side of the pond for 48hrs so that any aquatic creatures can crawl back into the pond and then consign it to the compost heap.  

The other option is to use a pond duckweed treatment but this can take a few weeks to work.