Barley straw is a home remedy for killing and preventing the growth of algae in ponds. There is conflicting evidence about the effectiveness of using barley straw as an algaecide. The United States Environmental Protection Agency has not approved the use of barley straw as a pesticide and it is illegal for vendors to promote barley straw as a pesticide.
Legal Status
Certified commercial applicators, garden and nursery companies, and lake management companies are forbidden by law to sell barley straw if they promote it as an algaecide or use the phrase "controls algae" as a selling point, according to Ohio State University. Barley straw is not regulated by the EPA as a pesticide. Furthermore, individuals are forbidden to use barley straw in water designated by the EPA as "public water." For example, an owner of a private pond can use barley straw, but individuals who live near a public lake cannot use barley straw in the water near their houses.
Theories/Speculation
Research in England shows that barley straw hinders the growth of some types of algae while research in the U.S. is inconclusive regarding the effect of barley straw on algae, according to Ohio State University.
One theory behind using barley straw to kill algae is that barley straw releases chemical compounds in freshwater. These chemical compounds, called phenolic compounds or lignin, do not kill existing algae, but prevent the growth of new algae, according to Water Gardens International.
The website also presents a different theory suggesting that barley straw releases carbon which feeds the microbe population of the water. Microbes limit the amount of phosphorous in the water, thus limiting the amount of phosphorous available for algae.
Best Barley to Use
Fresh barley and barley hay release nitrogen and phosphorus into the water which enables algae to grow. Fresh barely also decomposes at a faster rate than barley straw, reducing the amount of oxygen in the pond. Ohio State University recommends using dried barley straw instead of fresh barley or barley hay.
Amount of Barley Straw to Use
Ohio State University recommends using 0.025 lbs. of barley straw for every square yard of your pond's surface area. Place the barley straw inside a weighted mesh bag then place the mesh bag in the water.
Ponds that are at least 1 acre or 4,840 square yards require between 6 and 9 bags of barley straw evenly distributed around the perimeter of the pond. Break up a bale of barley straw and place 1/3 of the bale into a weighted permeable bag. Attach a rope to each bag so you can retrieve them when it's time to replace the barley straw. Place the bags in water no deeper than 6 feet because a majority of algae production in a pond occurs in shallow water.
Time Frame
Water Gardens International recommends placing the barley straw in your pond in April to prevent the growth and reproduction of algae that occurs as the weather warms. Barley straw will decompose in four to six months at which time you can replace the straw in the mesh bags.
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