How can I kill duckweed?

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Duckweed is:

  • A free floating plant that has 3 tiny leaves attached to its own root.
  • It is very fast growing
  • Unwanted by most pond owners as it will spread too far, too fast and completely cover the water unless controlled.

To get rid of duckweed you must remove it:

  • You cannot kill duckweed safely in the pond.
  • Physical control is the organic, wildlife-safe method of duckweed control.
  • You cannot use any chemical controls to kill the duckweed as these are not selective and will harm any other plants in your pond.

Everyone wants plant growth across the surface of a pond for shade but not Duckweed - Lemna minor. Better to choose the right size waterlily for surface cover in Summer and Aponogeton distachyos for cover in Winter.

  • Duckweed keeps growing until it takes over the entire pond
  • It will starve the submerged water of too much light & stop the activity of oxygenating plants.
  • This creates a poor environment for wildlife below the surface.
  • Best to remove it as soon as you see any.


To remove duckweed from your pond:

  • Take out every last piece or it will spread back.
  • Use a net or a tea strainer in a small container pond.
  • Wash every plant carefully from an infected pond.
  • Remain vigilant to remove any plantlet as soon as you see it.
  • Birds' feet can bring more in from a nearby pond.
  • Duckweed can drop seed to the base of the pond in Autumn to reappear in Spring.

Or use a skimmer to constantly remove it:

These are the 2 versions of electric skimmer unit available.

  • Attach the Oase unit to a spare outlet on an existing pump. This way the skimmer can be as powerful as your pump will allow.  By sucking water in it creates a vortex and the duckweed is pulled into into the mesh collecting basket. you then need to empty this on a regular basis.
  • The Velda unit comes with its own pump and floats on its own. There is no choice of pump size. But it is easier to fit - just place it on the water. It may not have such a good 'pulling power' to bring duckweed to its collecting basket as the Oase unit. But it does collect constantly the power is on. The collecting basket will fill up and need emptying onto the compost heap.
  • Skimmer units are also useful for 'sucking in' fallen leaves in Autumn so they do not fall to the bottom of the pond.