How to Make Your Own Pond Algaecide

Updated July 19, 2017

Ponds have become a popular landscape feature in the last decade. Whether natural or artificial, ponds provide the comforting sound of moving water, a home for interesting aquatic plants and colourful fish and--a place where green scum thrives. With the right conditions this scum, better known as algae, turns a pond into a large pot of odoriferous pea soup. Many pond owners resort to a chemical algicide to keep the water clean, but research indicates that a homemade solution, barley straw, may prevent algal growth in some ponds. Barley straw is most effective on filamentous algae, the long green strands that plague many ponds.

Calculate the surface area of the pond. If the pond is rectangular, multiply the length by the width. If the pond is circular, measure the radius, multiply it by itself, then multiply this total by 3.14 to find the area. For example, if a pond is 100 feet across, multiply 100 feet by 100 feet to get 10,000 feet. Multiply 10,000 by 3.14 to get 31,400 square feet. If the pond is irregular in size, determine if it is more rectangular or more circular, then use one of the above methods to calculate area.

Purchase the correct amount of barley straw. The rate to use is 0.011 Kilogram of straw per square yard of surface area. Barley straw is available at larger pond shops, some garden centres and on Internet sites that specialise in aquatic products. Barley straw purchased from a farmer must be in the form of dried straw, not hay.

Loosely place the correct amount of straw in a mesh bag--or bags, if the pond 's surface area requires more--and weigh the bag(s). The straw works best at the pond's bottom in water up to 6 feet deep. The decomposition of the straw releases a compound to help with algae control. Because this takes several weeks, put the straw in the pond in April, before algae growth begins. The straw does not kill existing algae; it prevents new algae from growing.


Research conducted in England has shown that barley straw can deter the growth of filamentous algae. Research in the United States is ongoing and not completely conclusive. Reading further on the subject is recommended.


Barley straw requires oxygenated water to work properly. An aerator may be necessary in some ponds. While it is rare, fish kill may result if oxygen levels are low.

Things You'll Need

  • Barley straw
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About the Author

Judith Allen has been a writer since 1980. She has contributed to the "Cambridge Encyclopedia of Latin America and the Caribbean," "Brava Magazine" and the "Middleton Times Tribune." Allen has a Master of Arts in history from the University of Wisconsin and is the owner of Eastside Gardens, LLC in Madison, WI.