Recent Reports and Tests
British researchers at The Institute for Arable Crops Research, Centre for Aquatic Plant Management (CAPM) in England, recommend applying barley straw to water to control algae. According to the Centre, their method "has been tested in a wide range of situations and in many countries and has proved to be very successful in situations with no known undesirable side effects." Further research suggests that lavender stalks, in combination with barley straw, enhances the effect of the barley straw and is particularly beneficial in ponds with pumps.
According to Susan Robins’ research article, Washington State University, Master Gardener, "the success of barley straw and lavender has been experienced in local San Juan Island ponds where it has been placed as a test.
Research at the San Juan Island ponds has found that lavender in combination with barley can be even more effective in the well-oxygenated water commonly found in ponds with pumped water circulation and/or fountains. Blending barley straw with lavender stalks in various proportions allows one to cover a range of water habitats from still lakes to pumped ponds.
How Barley Straw Works
As simple as it sounds, there are some basic rules to be followed for the method to work. First, an understanding of how it works is desirable. According to the CAPM, "when barley straw is put into water, its cellular structure starts to break down or decompose. A microbial activity process drives this breakdown or decomposition." It is during this process that chemicals are released which inhibit the growth of algae.
The decomposition is temperature dependent, being faster in the warmer waters of summer than in the cold waters of winter. Bacteria begin by breaking down the Lignin, which is the starchy material that makes straw stiff, and other cell wall components of the barley. After about 2 weeks the active microbes change from bacteria dominant to fungi dominant. As this process continues humus develops, (rotting) which is then transformed into a humic acid.
The humic acids are referred to as Dissolved Organic Carbon, DOC. DOC is a natural part of many fresh and saltwater ecosystems. As the acid leaches into the water it interacts with sunlight and dissolved oxygen and becomes unstable, decomposing into 2 single oxygen radicals. Thereafter, the oxygen radicals form a super-oxide radical, which then forms hydrogen peroxide in water. The hydrogen peroxide is more stable and long lasting in freshwater. The breaking down process of the barley then forms a continuous supply of the right form of DOC whereby the oxidizing agents can be continuously produced.
According to the CAPM, "Concentration of hydrogen peroxide of only 2 ppm peroxide have been demonstrated to inhibit the growth of algae." Some reports determined that barley straw might also act as a clarifier by flocculating fine particles in water.
How to Apply Straw
The CAPM states that the production of anti algal activity is only produced when the straw is rotting under well-oxygenated conditions and is near the surface of the water to properly mix with sunlight and dissolved oxygen. Straw should be loosely packed to benefit the breakdown process. Bales are too tightly packed and therefore do not allow for sufficient water movement through the straw, which will progressively become anaerobic (without oxygen) and may actually be a hazard.
Pellets sink, break down quickly and can become a mess at the pond bottom, thus creating the very problems you want to alleviate. Since the chemicals are only produced near the surface, barley that sinks or is too tightly packed will have no useful effect. Further, according to the Center, anaerobic decomposition can produce chemicals, which actually stimulate the growth of algae because the algae can use them as a source of carbon.
The production of hydrogen peroxide from the straw and lavender will continue until the decomposition process is almost complete—a process that generally lasts about four to six months. Hydrogen peroxide in low concentrations such as those produced by the above process has not been associated with any negative effects either on higher plants or on invertebrate animals and fish.
Although other straws such as wheat and corn stalks have some algaecidal properties, barley has been found to be much more effective and to last longer, and the addition of lavender was found to enhance its effect.
Time to Effect Results
Once barley straw has become active, which usually takes between 2 and 6 weeks, the time it takes to become effective varies with the type of algae. According to the CAPM small single cell algae, which turns the water green, usually disappear within 6 to 8 weeks of activity. The larger filamentous algae, known as blanket weeds or string algae can survive for longer periods and may not be controlled adequately in the first season if the straw is added too late in the growing season when algae growth is dense. It is therefore, preferable to add the straw very early in the spring before algal growth starts. Barley Straw should be replaced approximately every four to six months or sooner if the straw fully decomposes before that time.
How Much Straw to Use
The CAPM found that the most important measurement in calculating the quantity of straw required is the surface area of the water. The volume of water doesn’t appear to affect the performance of the straw as might be expected. This is because the majority of algae growth takes place in the surface layers of the water and so it’s not necessary to measure the depth of the water or its volume when calculating the quantity of straw needed.
In still and small pond waters the dosage of straw should be 50 grams (approximately 2oz.) per square meter of water surface area. Once the algae problem has been reduced, continued additions of straw should be maintained throughout the year. If the straw starts to smell, it should be removed and replaced. It is an indication that there was too much straw for too little water.The re-discovery of this completely organic and non-toxic solution to an ugly problem that affects most pond or lake owners is truly welcome.