Easy Way of Removing Blanket Weed in your Garden
Question: I have had a problem with duckweed in my pond all summer and would really like to get rid of it. My pond is quite natural in appearance, but still has a filtration system, and certainly does not lend itself to a pergola. I was wondering if any of the blanket weed treatments on the market would help, or does duckweed need a specific treatment, and if so what?
Oliver Borrow, Bracknell
Duckweed is the common name for any of the species of the tiny floating plants LEMNA, Lemna minor being the most common. They can be found virtually anywhere in the world in pools and ponds with nutrient rich to stagnant water.
They consist of just a leaf or two floating on the water, with one small root dangling down below the surface. The speed at which these leaves divide and thus propagating new plants and so cover a pond in less than a season is what makes them a pest for many pond keepers, obviously for the reason that they obscure the view of inside the pool. However it is likely that if the duckweed was not present, algae may be taking advantage of the light and nutritious by-products of a vibrant active pool.
This is the main reason you might actually still see it for sale in some aquatic centres because, particularly for new ponds, it does provide rapid pool cover and use up excessive nitrates, inhibiting the growth of algae whilst the higher plants in the water garden get themselves established and start doing a similar job.
There is a touch of Murphys Law here because there are some people who keep a stock of it because they find it a useful supplement to the diet of their fish, but you, being a pond keeper who does not like it, have fish of a similar disposition.
Perhaps your fish are not yet big enough.
If you have carp, try feeding them less and see if they will try a bit of salad on the side. Otherwise try some fairly large goldfish, but dont try Grass Carp, although they will eat it. Grass carp just make a mess in other respects so unless the pool is pristine and plant-less, in other words, there is nothing else to make a mess with, ignore the suggestion.
Actually, I grow a bit in one of my water butts because our ducks go absolutely crazy for it and eat every speck of it and then quack for more hence the name I suppose. But ducks make a mess of all but the largest water gardens.
I suppose even borrowing a duck would be out of the question? In fact the duck method of getting rid of blanket weed is typical of the problems that many methods of getting rid of it might cause i.e. damage to the plants in the rest of the water garden. It would be true that some of the more basic and old-fashioned algicides would knock it back but they would also have a detrimental effect on the rest of the plant life in the pool.
Also any dead duckweed would just sink to the bottom, and in the process of rotting, provide nutrition for another generation of duckweed spawned from the inevitable few surviving plants from your previous holocaust. The same would be true of using a glysophate weedkiller, which surprisingly would be less polluting but even more likely to affect other plants from the inevitable drift; a course of action one could only recommend for lakes.
The only other method that will keep the pool surface free of duckweed without your persistent activities with a net would be to resort to technology in the form of a skimmer. After doing some work in the States recently, I have realised that these are pretty ubiquitous over there since the idea of netting the surface of the pool is just too much effort to contemplate.
Backyard ponds are what they are referred to and they are generally too big to reach across anyway, so skimmers are built into the design from the start. Oase retail a portable and adjustable one that is an extension of one of their pumps that can be placed in any part of the pool. They would be available anywhere that sells Oase products even though they may not carry it as a stock item.
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