Duckweed can be common, and a real nuisance for pond owners. Often accompanied by the smaller plant watermeal, if left unchecked it can rapidly multiply and can soon cover your pond surface to the extent that it will start to starve the pond water of oxygen, leading to ill health and even death of fish in the worst of cases.

Duckweed is most often found in nutrient rich ponds, where a build up of dead leaves and other debris fallen to the pond bottom creates a sludge that becomes a food source for the duckweed. Older ponds or those in quiet undisturbed areas are more susceptible to duckweed.

Duckweed - Facts at a Glance

Common name: Duckweed
Botanical name: Lemna minuta, L. gibba and L. minor
Areas affected: Ponds and water features
Main causes:Floating weed
Timing: Lemna minuta seen year round, other species seen late spring to autumn; treat when seen

How to Deal with Duckweed

The old adage that prevention is better than cure certainly applies where the dreaded duckweed is concerned. However if duckweed has already begun to take hold you need to address the issue before your pond becomes overrun. There are a number of ways you can tackle this perennial problem.

The first thing to do is to use a net, rake or other equipment to physically remove the duckweed on the surface. You should also use a pond vacuum to remove all of that nasty sludge on the pond bottom. Through the autumn and winter you could cover your pond area with netting to prevent falling leaves and debris entering your pond and sinking to the bottom.

Another good idea is to aerate your pond using a pond air pump. This will add movement to the water and distribute oxygen more evenly. Aeration that extends to the bottom of the pond can disrupt the cycle of sediment build up.

Finally, if you still have some remnants of duckweed after performing the above steps you can turn to an anti-duckweed treatment. There are several types of these available such as Ecopond Duckweed Control and Blagdon Duckweed Buster. Both these treatments are completely natural and will not harm fish or other animals, and will not inhibit plant growth.

So to sum up – prevention is better than cure. Use netting to prevent leaves etc entering the pond in autumn and winter. Then use nets and tools to remove existing duckweed. Increase aeration in the pond, and finally if necessary introduce a natural anti-duckweed treatment to deal with any nuisance duckweed still remaining.