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We started our small pond last spring and it was as clear as a bell all summer and then all of a sudden about late December the dreaded blanket seed started appearing, now the poor pond is virtually covered! What is the best way to get rid of it? I don't really want to use chemicals because we have 8 goldfish in it. Does barley straw work as well as i've read? and would it be best to completely empty the pond, get rid of the weed and start again, introducing the straw? I have a one lilly and some marginal plants and the pond is serviced with an ultraviolet  filter, pump and fountain

Any suggestions gratefully received!

Shrinking Violet

Blanket weed is the very devil to get rid of!  You can never eradicate it, in my experience, but the best thing is to try to keep on top of it.

First - use a stick to twirl it around (like trying to get candyfloss on a stick!) and dispose of the weed.  Then ensure that the pond is as clear of it as possible - and for this, yes, barleystraw bales are pretty good.  Also use watercress!  If you can get hold of proper watercress bundles (remember the bunches sold on market stalls?) chuck them in, and leave for a couple of weeks.  Dunno why or how it works - but it does!  Keeps the dreaded blanketweed at bay, and can easily be removed.  But even this is not a cure-all you still need to be vigilant, and the stick twirling may still be necessary.


Hallo Sloeberrysal

We had the same problem and bought the following from Thompson & Morgan:

It's not cheap, but worked extremely well. Try and remove as much of the weed by hand as suggested above first. You might have to do it twice a year, but can thoroughly recommend.

There's nothing worse than a green pond!


Oh, forgot to mention, when you open link click on the GB part top right (page I gave you is for overseas!) Search Pond-Wizard!

And try to grow water lilies and other plants to cover at least 40% of pond surface. Prob wrong on that % but it's what I always aim for. Sunlight helps algae and blanket weed to grow. Oxygenating plants too are important so make sure ??ou have plenty of those.
Fish too create conditions for algae to may sound cruel but I cut out fish food and the fish then ate the algae.
Prb wildlife folk will think me mean......but, have you seen the cost of fish food lately?



Verdun we bought a big bag of koi food a week before someone nicked all the fish...

The watercress absorbs the nutrients which the algae feeds on and starves it. It's amazing how well it can work. Verdun's right about the oxygenators -they're a must -but they can be invasive too so keep an eye on them especially as it's a small pond. As with most things, maintenance is the key.


Watercress in bags from the supermarket always has a few roots or can be persuaded to grow some. That's where mine came from. It's going very well at the moment. The algae in the pond without the watercress is thicker.

Thanks everyone  this has been really useful advice.

At my wits end as the blanket weed was smothering one of the water lily growth despite all the stick twirling,  logs of straw and clearing oxygenators to which it was clinging. Weeding the pond!

Took out the affected lily and cleaned it up last night, also cleaned the area before putting it back.

Other lily pads are beginning to cover the pond but will certainly buy some watercress today.

If u have a filter clean it out  every 3/4 days - once the levels of watercress, Lily's etc are right the pond will settle again. Take out any leaves as soon as they land and take out any old debris that has rotten in the bottom. Make sure any potted plants have stones on top to stop soil from escaping. Blanket weed feeds on nitrogen so keep out all soil from garden falling in and only top your pond up with waterbutt water no tap water as it makes algae bloom.

Oh and no need to feed fish - they can live on all algae, watercress, gnat larvae etc.  They won't starve, by actually feeding them food u encourage extra waste and add to your problem. I wasn't sure about not feeding fish but it works. Having started a pond a couple of years ago , it all looks after itself and I've not fed my fish - they are breeding and living healthy & happily. 

A bag of sainsburys watercress works the best- some fish website did a trial a while ago of supermarket cress and it came out tops,  just throw it in!  even add to a waterfall if you have one as it works as an extra filter as the water passes.  You can thin it out when it eventually gets too big & it over winters so a bag lasts a lifetime 

Many thanks Foolio  

there are borders close to edge so dug shallow trenches and filled with pebbles. Topped up the two baskets I could reach with grit. Will check the larger one today.


Foolio comments about tap water were interesting - Our pond has always suffered quite badly from blanket weed (like a green slimy stuff that lies just under the surface)  At the beginning of last year I diverted some of the water from our roof to flow into the pond at one end and then back out of the pond at the other side and into the drain, the idea being to keep the pond freshed with rain water rather than topping it up with the hose.  The volumes are huge, I estimate about 40 ton of rain water will go into the pond anally.

Anyway, this year we have had no blanket weed whatsoever, not even a tiny bit - instead I think we have "Duckweed ? (a small leaf with a root dangling into the water) I keep reducing it but it does seem quite happy, hope its not going to be a nusiance.


Some very good advice above.

I built my pond about 30yrs ago 12' x 8'. Has a bio-filter and slate waterfall and a 30yr old lilly.

I tried stick twirling etc which helps. The lilly also now covers about 60% of the surface by late summer which now helps a lot. But I did have a big problem in the early days.

I was advised to try Cloverleaf blanket weed destroyer and much to my surprise it works amazingly well. Doesn't affect fish/plants or filters but within 3-4 days most of the blanket weed was dead. Of course you have to be careful not to introduce a further problem with a pond full of dead vegetation, so get rid of as much of the dead stuff as you can. There's another product under the Cloverleaf brand that also gets rid of the dead blanket weed if needed - I've not needed to use this.

I dose works for the whole season. I change 10% water every couple of weeks - doesn't affect how it works.

Pond Wizard is absolutely useless - total waste of money. Two doses and algae still keeps coming back. Followed instructions to the letter - cleared algae out before dosing and came back within a week!! Really cross with myself for being duped. Going to try the watercress, even if doesn't work it is a far cheaper mistake!


It takes a while to get rid of it naturally but go with the guidance I gave above and you'll get there. It's not an over night fix - it's a long term thing that eventually provides a harmonious pond   


Watercress works very well. I've always used it and it couldn't be easier - just chuck it in as Foolio says. If it roots anywhere you don't want it, it's easy to pull out. If it's a big pond and you can't reach all areas easily, you can always put it in a basket to keep it contained. It works because it absorbs the nutrients that the blanket weed feeds on. 

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