Barley Straw: Nature's Way to Rid Your
Pond of String Algae
Studies in England show that barley straw is a natural, low-tech way to keep
your pond free of string algae.
By Sue Speichert
Originally published in Water Gardening Magazine, March/April 1999
Reprinted with permission.
As the story goes, one warm and sunny summer day, a bale of barley straw fell into a
farmer's pond in Scotland. He wasn't particularly worried about the straw in the pond and
simply left it there. Several weeks later, the farmer noticed that there was less string
algae in the pond than usual. The farmer's haphazard discovery made its way to the Centre
for Aquatic Plant Management in England. The Centre undertook studies to investigate
whether the presence of barley straw in water could affect string algae and blue-green
algae. The studies confirm that barley straw does, in fact, stop the growth of all forms
of algae. According to the Centre's published findings, barley straw is a"cheap and
environmentally acceptable way of controlling algae in water bodies ranging from garden
ponds to large reservoirs, streams, rivers and lakes."
In a nutshell, barley straw works by releasing a chemical that inhibits the growth of
algae. It doesn't actually destroy algae that's already growing in the pond. Instead, it
stops the algae before it has a chance to get started.
Barley straw works it magic as it breaks down and decomposes in the pond. It's a
gradual process that's very temperature dependent, accelerating as the water warms. Once
the straw becomes effective, it continues to inhibit algae growth until the straw is
almost completely decomposed. As a general rule, the straw lasts for about six months.
According to the Centre, the precise way in which barley straw stops algae growth is
"not fully proven." The Centre believes that when the straw rots, lignins in the
cell walls are released into the water. The lignins oxidize into humic acids and other
humic substances. When combined with sunlight and dissolved oxygen, these humic substances
convert to hydrogen peroxide. Low levels of hydrogen peroxide have been proven to inhibit
algae growth. Peroxides only last a few minutes; you would need a constant flow of fresh
hydrogen peroxide into your pond water in order to keep algae at bay. When there's
decomposing barley straw in the water, the peroxides are continuously produced (given
sufficient sunlight and oxygen), and so the algae continuously inhibited from growing.
It's not known why barley straw works better than other forms of straw to keep the pond
free of algae. Yet studies have found that barley straw is significantly better at ridding
the pond of string algae and blue green algae, forms that beneficial bacteria is unable to
keep at bay.
Barley straw only works if it is put in the pond before the algae begins to grow. It
will not remove algae that is already present. Once the algae appears, it has to be
removed by other means for the barley straw to go to work. This means manual removal of
the algae or the use of some type of algaecide. Once the algae has been removed, though,
the barley straw will be able to keep the algae from returning.
When determining how much barley straw to use, the important consideration is your
surface area of water, not your water volume. The Centre recommends, as a general rule,
that pond owners use about .03 ounces of straw for every square yard of water surface. If
you've always had a lot of string algae, then you can use more. Once the algae is under
control, you can scale back as you gain more experience with barley straw's effectiveness
in your pond.
The best way to use barley straw in a backyard pond is to bundle it in a loose bag or
nylon stocking. You can attach a string with a weight to keep the bundle from floating all
over the pond. Remember, though, that as the straw becomes wet and waterlogged, it will
sink to the bottom of the pond. It's important to keep the straw near the surface, because
that's where there is more oxygen and also where the straw will have its greatest effect.
Attach a cork or a plastic soda bottle to the bundle to keep it afloat.
In large, natural bodies of water, whether ponds, lakes, or streams, the straw should
be loosely bundled in onion or potato sacks. It's better to use several smaller bundles
rather than one large sack. Place the bundles at intervals so that the most amount of
water surface is exposed to the straw's useful effects. In lakes, reservoirs, and ponds,
the bundles should be held in place with a weight and kept from sinking by use of a float
device. For streams, the bundles can be held in place at the shore and let to float out
into the water, again using a float device to keep the bundles from sinking to the bottom.
In a backyard pond, one or two bundles will probably be sufficient. If there is no
moving water, the bundle should be positioned in the middle of the pond, so that the
anti-algae chemicals are able to disburse outward in all directions. If there is a stream
or waterfall, then the bundle should be placed nearby, to take advantage of the increased
oxygen and the additional dispersion of anti-algae chemicals throughout the entire pond. A
header pool is an ideal location for a bundle of barley straw in a backyard garden pond.
It's best to put the barley straw into the pond early in the spring, so that it will
have a chance to break down somewhat before algae would appear. The warmer your climate,
the sooner you should place the barley straw in the pond. In mild or cool climates,
February or March would be optimal. As a very general rule, it will take up to a month for
the straw to become effective. When the water temperature is 70 F or warmer, the straw may
take only a month to spring into action. If the water is cooler than 60 F, it can take up
to 8 to 10 weeks for the straw to go into effect. Don't put in fresh bundles of barley
straw during periods of prolonged hot weather decaying straw combined with dying
algae may deplete the amount of oxygen in the water.
If you live in a warmer climate where algae can be a problem even in the fall and
winter, it's wise to place a new bundle in the pond in the fall before the old batch has
completely rotted away. This will allow the new straw to become effective by the time the
old straw needs to be thrown out.
As a general rule, new straw should be added every six months. This is just an average,
however, and it's best to keep a close watch on whether new algae appears to be taking
hold in the pond. Don't wait until all the straw is gone to add a new bundle. Add the new
one while the old bundle is still working, so that there is an overlap. That way, the new
straw will already be activated in the pond once the old bale of straw should be removed.
You can use straw in combination with algicides, either applying them when the straw is
already in the pond, or using the algicide first and then waiting a while before adding
the straw. The sooner you put the barley straw into the pond, the sooner it will inhibit
the algae's return.
The Centre's studies have found that barley straw has no an adverse effect on aquatic
plants or wildlife. In some cases, submerged plants have been able to grow better once
straw was applied, most likely because the absence of algae allows for greater penetration
of sunlight and facilitates photosynthesis in the plants. Straw has had no adverse effect
on invertebrates such as Water Shrimp (Gammarus spp.) which eat waste and debris. They
have been found to grow well and rapidly in the protected environment of the straw. Many
invertebrates are in fact a benefit to the pond, since they eat decomposing organic
matter, and some eat algae. As the straw decomposes and the number of invertebrates
increases, they float way from the safety of the straw bales and are consumed by fish or
birds, enriching the food source of these larger pond-lovers. Their numbers also increase
and health improves from the presence of the barley straw. Again this is likely because
the lack of algae allows for an increase in plant life and small animal life in the pond,
which is an important food source for the fish and birds.
Note from Aquarticles editor: Following this idea, some pond supplies companies
have come up with easy-to-use barley straw pellets. My LFS sells Laguna "Natural
Barley Straw Pellets," a 2 1/2 lb. bag of which treats 1250 gallons and costs about