Barley straw has emerged as a popular, natural method for managing excessive algae growth in ponds and other small water bodies. This approach utilizes the dried stalks of the barley plant to control both the free-floating planktonic algae that cause green water and the filamentous algae known as blanket weed. It is considered a chemical-free preventative treatment, working by inhibiting the growth of new algae rather than killing existing blooms. The effectiveness of barley straw is entirely dependent on a slow, continuous decomposition process that requires oxygenated water, making it a management tool rather than an instant solution.
The Specific Biological Mechanism
The anti-algal effect is the result of an aerobic decomposition process. Once submerged, the straw begins to break down, driven by bacteria and fungi that consume the organic material. This decay must occur in the presence of dissolved oxygen to function properly, which is why aeration is a factor in its success.
As the straw decomposes, it releases various organic compounds, including humic acids and oxidized polyphenolics. These compounds react, particularly when exposed to oxygen and sunlight, to generate trace amounts of hydrogen peroxide. This generation of hydrogen peroxide is believed to be the primary mechanism by which the straw inhibits algae.
The concentration of hydrogen peroxide produced is very low, making the process completely safe for fish, plants, and other aquatic life. This low-level oxidative agent acts as an algistatic compound, meaning it prevents new algal cells from growing and dividing. Barley straw is not an algaecide, and it will not eliminate a heavy, established bloom, but it suppresses the growth of future algae colonies.
Practical Application and Deployment
The straw should never be applied as a tightly packed bale, as this prevents water and oxygen from circulating through the material. Instead, the bale must be broken apart and the loose straw placed into mesh bags, netting, or cages to maximize its surface area exposure to the water.
The correct dosage is determined by the pond’s surface area, not its volume. A general recommendation is between 100 and 300 pounds of straw per surface acre, or roughly 0.025 to 0.1 pounds per 10 square feet for smaller water bodies. If a pond has a history of severe algae problems, a higher initial dose within this range may be necessary.
The straw-filled mesh bags must be suspended near the surface, ideally in the top three to four feet of the water column, and secured with floats or anchors. This ensures the straw remains in the highly oxygenated layer where aerobic decomposition can occur. Placing the bundles near areas of water flow, such as inlets or aerators, further aids decomposition and helps distribute the anti-algal compounds throughout the pond.
Optimizing Effectiveness and Timing
Barley straw should be applied early in the spring before algae naturally begin to flourish, as it works strictly as a preventative measure. Since the straw must first decompose to release the inhibiting compounds, the application must be timed correctly.
The speed of decomposition is highly dependent on water temperature. When water temperatures are below 50°F, it can take six to eight weeks for the straw to reach its effective level, but in warmer water above 68°F, activation can take only one to two weeks.
Once the straw begins producing the anti-algal compounds, it typically remains effective for four to six months. Leaving fully decomposed straw in the pond can be counterproductive, as the decaying organic matter may release nutrients that could fuel future algae growth.
Low oxygen levels or a high nutrient load can hinder the straw’s performance. If a pond has poor circulation, adding an aerator or fountain can improve oxygenation, which speeds up decomposition and enhances the distribution of the active compounds. Regular replacement every four to six months, often in the spring and fall, ensures a continuous release of the algae-inhibiting agent.