What is Blanket Weed and How to get rid of it

What is blanket weed

Blanket weed is an algae, it’s scientific name is filamentous algae, but it’s also know as string algae or silkweed.

It’s actually a long chain of algae cells that link together to form the string like effect.

It thrives on nutrients and can grow at about 2 metres a day and can also double in weight in a day which makes it one of the fastest growing algae in your pond.

Blanket weed looks like thick clumps of long green hair all matted together, it’s slimy, has no leaves, stems or roots.

It usually floats on the top of your pond like a blanket hence the name, it can also submerge itself.

Blanket weed can also restrict the amount of area your fish has to swim.

It can attach itself to rocks, the side of your pond or to beneficial oxygenating plants.

If it attaches to your plants it will reduce their oxygen levels by smothering them which is not good news.

Blanket weed also consumes vast amounts of oxygen which has an effect on plant and fish life within your pond.

Having blanket weed in your pond can be a real problem, once it’s established it will compete with other vegetation in your pond as well as competing for oxygen that your fish need to live on, it’s a real problem in warmer months. 

Birds and insects are known to bring algae spores to your pond which in turn turns to string algae, the spores can also be blown into your pond.

A pond in a sunny spot are more problematic than one in a shady area, the algae likes the warmth and bright sunlight which helps it grow faster, the more it grows the harder it is to get rid of it.

High levels of phosphate and nitrate in your pond along with organic waste will help in the growth of the algae.

If you have blanket weed in your pond it can also affect your pump and filter system causing it to block.

Although fish like to eat it they can also get tangled in the string algae, the sooner you remove it the better it will be for the health of your pond and your fish.

How to get rid of blanket weed

The first thing you should do is physically remove as much blanket weed from your pond as you can.

You can use a blanket weed brush like this one from Amazon.co.uk to do this.

Although this seems to be a good solution it can cause more problems further down the road unless you take further steps.

When you manually remove the blanket weed you risk releasing spores back into your pond, within a very short time these spores will grow and you will be back to where you started, so just removing it is not a solution.

When you remove the blanket weed leave it at the edge of your pond, this will allow any living insects to get back to the pond, also check to see if any creatures that you can help back into the water.

After a couple of days you can remove it from the side of your pond, use it on your compost heap if you have one or as a mulch around your garden plants.

As I have said physically removing blanket weed is not going to solve your problem, you’re never going to get rid of it all, so you need to take other measures otherwise you will be back to square one.

Use a treatment to get rid of the remains of the blanket weed and to keep it at bay.

You can use barley straw to deter blanket weed growing in the first place but it usually takes a while and can look unsightly, check out these products in our blanket weed treatment post.

To prevent the blanket weed returning there are things you can do.

Reduce the amount of nutrients in the pond by having lots of aquatic plants, these will absorb excess nutrients that blanket weed thrive on.

Do not overstock your pond with fish, the more fish you have the more waste (poo) will be produced which will lead to more nutrients.

Once you have eradicated the blanket weed from your pond you need to be on your toes because it can come back as quickly as you got rid of it.

If you see signs of it coming back treat it before it gets out of hand.