Does Barley Straw Stop Algae Growth in Ponds?

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Robert Pavlis

Algae is probably the pond owners biggest problem and people try everything to get rid of it, even barley straw. This is becoming a common method and companies are even selling bags of it for small back yard ponds, but does it actually work?

If you think about it for a minute, it does not make any sense. Why would barley straw work? Why not some other kind of straw?

Even if it does work, it seems a shame to use it in a pond rather than make beer out of it!

Does Barley Straw Stop Algae Growth in Ponds?
Does Barley Straw Stop Algae Growth in Ponds?

Using Barley Straw to Stop Algae

This seems to be simple. Take some straw. Throw it into the pond and voila. No algae.

How much should you use?

The recommended numbers are all over the map. One commercial product advertises that the “bag” treats 3,000 gal or 13,500 L. The bag is not labelled with a quantity. Pen State university says the volume does not matter; it is the surface area which is important. Why do suppliers not know that? Pen State goes on to say “The most common application is about two to three bales per surface acre of pond (or about 10 to 25 grams of straw per square meter of pond area) (1/2 oz per 10 sq ft).”

Plant Science for Gardeners by Robert Pavlis

Is all barley straw of the same quality?

Nobody seems to discuss the quality of the straw – maybe it’s not important. “A wide range of barley straw varieties have been tested, including some grown organically and they all produced similar levels of anti-algal activity.”

You can also use barley straw extract – get the benefits of barley straw without the mess. It is not clear to me how this product is made, but numerous suppliers produce it. It is promoted as straw in a liquid form.

Barley straw pellets are also available, but these sink to the bottom of the pond, and since they need to decompose aerobically (see below) I don’t see how they can work.

Barley straw works better than other types of straw, such as wheat straw.

Does Barley Straw Kill Algae?

The scientific reports are fairly consistent on this question; no it does not kill algae.

Does Barley Straw Stop Algae From Growing?

The answer to this question is far more complex. To begin with, it needs to be used in a specific way to have any chance of working. A lot of the social media descriptions miss some of the key points on using it. I’ll discuss some of these in the next section.

There are numerous studies that demonstrate barley straw slows down the growth of algae (ie it is algistatic and not algicidal). Most of the positive results come out of the UK. There are also numerous research results that show it does not work and many of these are done in the US.

I have no idea why there are differences between the countries.

One study showed that barley straw liquor (extract) worked a bit, but barley straw did not work. Some studies show an effect in the lab, but not in the field.

Building Natural Ponds book, by Robert Pavlis

One of the problems with much of this work is a lack of standardized testing methods for algae response and a lack of a standard product.

Conditions Required for Barley Straw to Work

barley straw
barley straw

Adding barley straw to a pond does nothing, until the decomposition of the straw reaches a certain stage. Reports talk about ‘conditioning’ it and this can take anywhere from a couple of weeks to a couple of months, depending on several factors, with temperature being one of the most important.

Once it is conditioned properly, it continues to work for several months.

Barley straw extract is already conditioned and starts working faster.

Need for oxygen

Barley straw needs to be conditioned aerobically with lots of oxygen available. It is suggested the straw floats on top of the water and not under the surface. The pond should be aerated or it does not work. This requirement would mean that barley straw does not work in natural ponds that don’t have aeration pumps or moving water.

Nutrient Rich Water

Barley straw seems to be less effective in water that has a high nutrient level. Which seems to indicate that it is less effective in large algae blooms since they have high nutrient levels.

Control of Different Types of Algae

The general public and many gardeners talk about algae as being one type of organism, but there are many species. Find out more about algae in the book Building Natural Ponds.

Studies that identified the algae species being tested found that some types are inhibited, some are not, and some types actually increase in number in the presence of barley straw. What this means is that you could be trying to use barley straw to control a species that is not affected.

It can be used to control some species of both single celled algae and filamentous (string) algae.

How Does Barley Straw Work?

Popular blogs report that barley straw works because as it releases hydrogen peroxide as it decomposes, which kills algae. That story is not completely true.

Hydrogen peroxide can kill algae, but the decaying straw does not produce hydrogen peroxide, at least not directly.

As the straw decomposes a variety of organic compounds are released, and many of these have NOT been identified. Some have been identified and have been shown to be algistatic, with 2 phenyl-phenol showing strong effects. These compounds can also react with sunlight and eventually produce hydrogen peroxide which may or may not play a role.

Science has not yet established which mechanisms are at play.

Does Barley Straw Work in Ponds?

It does not kill algae. It may control the growth of some species, but probably not all of them. Or it has no effect at all.

Barley straw is certainly not as effective as the suppliers indicate.

It will work best in an aerated pond and is much less likely to work in a natural pond with no aeration. Depending on temperature, it can take 2 to 8 weeks before it starts working. Extract starts working sooner, but there has been little testing of commercial products. Barley straw pellets probably don’t work at all.

If you have an algae problem, it may be worth trying, but don’t expect miracles. I think it is much better to design the pond correctly so that algae growth is not a problem.

More Articles About Ponds:

Pond Pumps and Pond Filters

Beneficial Pond Bacteria – A Waste of Money

Water Lilies – Hardy and Tropical Water Lilies for Ponds

Winterizing Ponds and Water Features

10 Ways to Control Duckweed in Your Pond

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

16 thoughts on “Does Barley Straw Stop Algae Growth in Ponds?”

  1. What about black pond dye? It’s claimed that it “blocks light, denying algae its food source.” It seems to me that it would make no difference to algae which floats on (or near) the pond surface, only on sbmerged vegetation.

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  2. Does barley extract prevent string algae? I’m doing a thorough cleaning of my pond and will start fresh. I would like to prevent string algae. I’ve found that introducing submerged and surface plants overtakes the pond and I can’t see the fish or even most of the water, the ‘good’ ones seem to be very invasive. And my pond is in direct sunlight most of the day in hot Arizona.

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  3. Farm kid here. The opening paragraphs of this article are embarrassing.

    “If you think about it for a minute, it does not make any sense. Why would barley straw work? Why not some other kind of straw?“

    The implication being I suppose that all straw is identical and therefore the type does not matter. While it is true that most straw comes from various types of grasses – barley, wheat, rye, and oats all provide us with straw – there is also flax straw. Which comes from a flowering plant. This is rather like asking a chef why you can’t use carrots instead of beets. They are both root crops but there the resemblance ends. Barley straw and flax straw are both dry plant parts but thinking that any straw could be used when barley straw is specified is as silly as making borscht with carrots.

    Someone else has already pointed out the second problem but I’ll mention it too: “Even if it does work, it seems a shame to use it in a pond rather than make beer out of it!”

    Really?

    Do you think beef and barley soup is also made with barley straw?

    Straw is a waste product that we have frugally found many uses for. We don’t grow barley for the straw any more than you grow roses for the thorns.

    I think your ambition is good: use science to demolish myths. That’s a fantastic goal. But I also think that your impressive credentials have fooled you into believing that whatever you think you know about a subject is correct. This problem is evident on other pages too. (The lengthy comment section on the “don’t feed bees” page comes to mind.)

    The science may be sound. But the nonsense that surrounds it casts serious doubts on its validity. Get your fluff paragraphs right so that people can trust your content paragraphs.

    Reply
    • “Even if it does work, it seems a shame to use it in a pond rather than make beer out of it!” – clearly that statement was made tongue in cheek. I guess you missed the subtleness of it.

      So you think barley straw has some special properties that make it more suitable for this application than other straw – but you failed to mention even one of those! So maybe it is not different than using other types of straw?

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  4. Most garden ponds if they are well managed and plants have naturalised eventually become clear. I suspect that many of the success stories are just a consequence of time.
    I have to confess that my own pond when i have to top up with tap water which always here contains unfortunately some nitrogen impurity that I do get some blanket weed. I occasionally scrape some out with my lawn scarifier. Around the blanket weed the water is crystal clear!

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  5. I had a problem with algae. Have long hours of harsh sunlight and heat in summer (The Karoo, western cape in South Africa). The pond (+- 20 000 litre) is on a lei water system and stores water for my sprinkler system. The water is used and the pond refilled (topped up) twice a week. The income water is infested with Algae and string algae and is rich in minerals . The water was often green and discoloured. There are about 50 koi fish, tilapia and gold fish that live in the pond. I Installed water lily’s and reeds. After reading about the barley straw, I put in one bale, wrapped in chicken wire to hold it together and weights to keep it at the bottom (it floats like a cork). After about a month , as it started to decompose the water started to clear. It does not kill algae but it does stop it from growing / multiplying. In combination with the reeds and water lily’s my pond is crystal clear, the fish like to congregate and hover over the top of the barley. I have to replace the barley straw annually. So definitely works for me.

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    • How do you know it was the straw and not the plants?

      According to the science – it does not work at the bottom of the pond.

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  6. I have used barley straw in the UK, by the way its is strqw not hay and therefore contains no grains, it is a bi product of harvesting the grains to make beer. We used to stuff old stockings with it, float that in our pond and it kept the green algi in check, it did not help hugely with what we called blanket weed though. The UK environment agency used barley straw bales in stream to control algea and also if there was a spill of any description it was the prefered clean up agent acting as huge filter mediums.

    Over 15 years the results we got in our 10 x 5 x3 foot pond did strongly suggest there is something in it. As to if it would work down here in Australia, I need to test it. I have a non scientific gut feeling that both water and air temps come into play, hence whynthe UK get such good results. So with our temps here, it may possibly create an issue with dissolved O2 content, exasperating the situation.

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    • The problem with testing by home owners is that they rarely have two equal ponds to use – one with straw and one without. Without a control you can’t reach any conclusions.

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      • I had a serious problem with string algae Feb/March 2022, without treatment it was running rampant, I introduced a small bail of barley Straw ‘A’ grade. That was two weeks ago, now it’s all but gone and I can see my fish again!

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  7. I would say – completely a priori, and not having read anything about garden pond planning – that if you don’t want algae in your pond it should have vascular plants which remove nutrients from the water – either the pink billows of roots of tree Willows, or herbaceous plants which you harvest out of the pond to reduce the net nutrient levels.

    Reply

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