how to control duckweed.

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Its got single round leaf with a small root below
single round leaf with a small root below
  • What is Duckweed
  • How to recognise duckweed.
  • where does it come from?  
  • how to control duckweed.  
  • How to prevent duckweed getting into my pond.
  • What's the problem with duckweed.
  • Is duckweed good for wildlife ponds?

What is the little green plant floating on my pond ?

It's Duckweed, a tiny single free-floating aquatic perennial weed, that if left uncontrolled, can quickly and completely cover the water surface of still and slow moving water, forming a green ‘carpet’ on the surface of the water. Duckweed grows in nutrient-rich waters and is common in garden ponds.
Its got single round leaf with a small root below and is about 0.5cm (¼in) diameter ?
How does duckweed spread so quickly?
In Summer it reproduces by growing  two or three tiny baby plants that bud from the original, these seedlings then reproduce new plants in the same way. In a nutrient rich pond, the plant mass can double every few days, quickly covering the surface of a garden pond.
How to prevent duckweed getting into my pond.
The introduction of duckweed into garden ponds is almost impossible to stop, it can be brought in with new water plants. Duckweed can also be brought in on the feet of  birds even frogs visiting from a near neighbours pond. The only way to stop it suffocating the pond is to control it.
Controlling duckweed the non chemical way
On small ponds continuous netting keeps the weed under control.
Larger ponds, using a floating boom to sweep from end to end and then removing the mass with a large strong net works. Duckweed makes great compost, providing its composted away from the pond.
Planting Waterlilies and other plants with floating leaves will also reduce the level of duckweed.
Waterfalls and moving water, will push the weed to one end of the pond making it easier to remove from the pond.
Reduce nutrients in the pond. 
Because duckweed grows in nutrient-rich waters, probably the single most important thing you can do to keep duckweed to a minimum, is to stop over feeding your fish. Stop adding fertilisers to make your pond plants grow, they don't need it, fish, frogs, newts all pooh in your pond, providing all the fertiliser your pond plants need to keep them healthy.
Unless its a newly built pond and the substrate needs to build up, removing leaves before they rot and sink to the bottom will also help reduce surplus nutrients.
Control with chemicals and bacteria .
There aren't any chemical weedkillers available to the public. Some garden and water garden retailers are selling a product called 'Duckweed Control' it contains a bacterial culture that removes nutrients from the water to discourage duckweed. They say it's safe to use in garden ponds and won't harm any of the animals including newts and frogs at various stages of development, plus stacks of invertebrates. 

On the label it says "eco friendly" and "frog friendly" and "contains selected bacteria" and "suitable for use in all types of ponds". It doesn't have a list of active ingredients, though it does say "wash hands after use" and "keep out of reach of children".

I would be scared of damaging the eco-system  in my 'wildlife' ponds. I prefer instead to control the duckweed and be sensible with nutrient control.
What's the problem with duckweed.
It's not a problem if kept under control, It provides shade, some fish eat it, pond insect life love it and its not unattractive floating on the surface of a nature pond.
Is duckweed good for wildlife ponds?
As I have said above, If controlled it can be beneficial to a wildlife pond.
But uncontrolled duckweed is a problem,  If the surface is completely covered sunlight is shaded from getting into the pond. All living things need light to survive, so totally shading  out sunlight  would kill off  plants, invertebrates and other pond-life living in the bottom of the pond. They would die and decompose using up any oxygen that  was getting through the duckweed. Eventually Killing off the ecosystem, leading to the death of the pond. Meanwhile the Duck Weed would continue to grow.
I have seen this happen in wild ponds, leaving only the duckweed and marginals living and of course the ducks.