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!
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).”
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.
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
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.