OK, I admit it, this is click-bait: there is NO WAY to quickly and easily remove duckweed from a pond, without using chemicals. And even then, it's not quick.
But there is a way to massively reduce your duckweed burden, quickly, easily, and without the use of any chemicals at all.
It won't clear all of it, which means that it WILL grow back: but it gets it under control.
By the way, when I say "duckweed", I'm not sure of the exact botanical name, and there are several different common names for it, but we all know what it is - those small, floating green bits that multiply until they are pretty well covering the surface of the pond.
In fact, in one of "my" gardens there is a pond where the duckweed is so dense that the surface of the pond looks like lush green grass, and we all think that one day, an unsuspecting visitor is going to attempt to walk on water, and will get a very nasty surprise.... and this is why I started doing research into ways to remove the wretched stuff.
Now, if you are struggling with a similar mass of duckweed, here's some good news for you - apparently a good thick covering of Duckweed does prevent the growth of blanketweed.... but that's about all I can find in favour of it!
Some sites suggest that covering the surface of the water with, for example, water lily leaves, will reduce the duckweed, as will creating movement within the water, ie from a small fountain, or a solar-powered pump to recirculate the water in such a way that it splashes back down into the pond, to create as much disturbance as possible.
Please note that it is not possible to combine these two ideas: lily leaves don't like disturbed water.
(Personally, I rather think that the duckweed would just fill in any gaps around and between the lilies, so I don't think that idea would really work very well.)
Most pond websites agree that duckweed forms on ponds with too much in the way of nutrients (the rich sludgy stuff at the bottom), and not enough water movement/aeration, and is worst in ponds which are sheltered from the wind, and which don't have any flow, ie are self-contained. This probably describes most "garden" ponds!
So, what do we do with duckweed?
The best advice seems to be, to manually remove as much as possible (nets, scoops, running a boom across the pond), before applying chemicals: but of course most of the chemicals which are available will also kill all your aquatic plants, along with most of the wildlife.
So we don't like chemicals in our ponds... oh, having said that, there is reputed to be one eco-friendly duckweed destroyer, which is said to not harm the other plants or the wildlife ...but it doesn't "kill" the duckweed, it just prevents it from multiplying, if I am reading the instructions correctly: and they emphasis the need to manually remove the bulk of the weed first.
Not a great deal of use, then.
What is my great How To idea then?
Simply put: over-fill your pond.
All I did was to take the hose, run it into the pond, and let the water run until the water spills over the top, taking all the floating duckweed away with it.
It was miraculous! And it watered the grass, at the same time!
Having turned the tap off, I left it to sit for a while, during which time a lot of little bits of duckweed floated to the surface, so those were scooped out with the net.
It is worth mentioning that we also took out the plants, and gave them a good hosing off, over the grass: otherwise the rising water level leaves a ring of duckweed around every vertical stem. Mind you, those little bits will then dry out and die off... so does it help? This point is open for debate, do please feel free to add your thoughts, below!
Also to be borne in mind is the life cycle of duckweed: those individual floating leaves start off life rooted into the plants, so once you have flooded off the top layer, it is worth gently agitating any submerged plants, to loosen off the rooted duckweed strands. Once they float to the surface, they can be scooped out with a net, or you can just add a bit more water, and flood that lot out as well.
Yes, on a big pond, it will take a lot of water, but if you have a lot of water butts (and if you don't - why not??!!) then
you can clip a hose onto the water butt tap, and use that water, which
is free, and is probably "better" for your pond than the chlorinated
(and expensive) tap water.
And there you have it: compared to all the hours I have spent scooping with a net, this method is quick, simple, and very eco, especially if you use the water butt water.
Oh, and it's far, far better for the pond's wildlife - instead of all that scooping and banging about with nets, heaving plants in and out, and so on: just let the "tide" rise up to the top, and then let it settle naturally back down again.
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