Excessive algae growth is a common challenge for owners of ponds, lakes, and ornamental water features. Uncontrolled growth quickly turns clear water into a murky, green soup, causing aesthetic issues and potential problems for aquatic life. For decades, barley straw has been suggested as a natural, chemical-free method to manage this issue. This traditional technique involves placing the straw into the water, offering an environmentally friendly alternative to chemical treatments. The central question is how the decomposition of this simple grain residue manages to keep water clear.
The Algae Suppression Mechanism
The effectiveness of barley straw does not come from the straw itself, but from the complex chemical processes that occur as it slowly breaks down in the water. For the anti-algal effect to be produced, the straw must undergo aerobic decomposition, meaning the process requires a substantial amount of dissolved oxygen. This decomposition is largely driven by fungi and bacteria, which break down the barley cellulose and lignin.
As the straw rots, it releases various organic compounds, including humic acids and oxidized polyphenolics, into the surrounding water. These compounds are considered precursors to the active alga-inhibiting agent. Crucially, in the presence of sunlight and oxygen, these breakdown products convert into low, sustained concentrations of hydrogen peroxide.
Hydrogen peroxide is a mild algaecide, but the concentrations produced by the straw are low enough to be harmless to fish and established aquatic plants. This mechanism is algistatic, meaning it prevents the growth of new algal cells rather than killing existing, mature algae blooms. The straw inhibits the reproductive capability of the algae before a full bloom can develop. It takes several weeks for decomposition to begin and for peroxide levels to reach a concentration that suppresses algae growth.
Practical Application and Placement
To ensure the decomposition process is aerobic and the active compounds are distributed effectively, proper application is necessary. Simply tossing a compact bale into the water results in anaerobic conditions in the center, halting the production of desired compounds and potentially depleting oxygen. The straw must be broken apart and placed loosely into a mesh bag, net, or porous container that allows for maximum water and air circulation.
The recommended dosage depends on the surface area of the water body, not the depth, because sunlight and oxygen are concentrated near the surface. A common application rate for a body of water with a history of algae problems is approximately 225 pounds of straw per surface acre. For smaller ornamental ponds, this translates to roughly 25 to 50 grams of straw for every square meter of surface area. Higher initial doses, up to 450 pounds per acre, may be necessary for water that is particularly muddy or has severe, chronic algae issues.
The netting filled with straw should be anchored and floated just below the water surface, ideally in the top three to four feet of the water column. Placing the straw near areas of high aeration, such as a waterfall, fountain, or near an existing aerator, helps to maximize the necessary oxygen flow for decomposition. Application should occur in early spring before algae growth typically begins, allowing time for the straw to become active. Once decomposition starts, the barley straw remains effective for four to six months before it needs to be replaced.
Factors Affecting Efficacy
Water temperature is the most significant variable affecting the decomposition rate and the time it takes for the treatment to become active. In colder water, below 50 degrees Fahrenheit, it can take six to eight weeks for the straw to begin producing the anti-algal compounds. Conversely, in warmer water above 68 degrees Fahrenheit, decomposition accelerates, and the straw may become effective in as little as one to two weeks.
The level of oxygenation in the water is another major factor; highly stagnant water or ponds with low dissolved oxygen will significantly slow the necessary aerobic breakdown. Furthermore, the type of algae present affects the outcome, as barley straw is generally more effective at controlling unicellular, free-floating algae, which cause green water, than it is against tough, filamentous varieties. The presence of excessive suspended sediments, commonly referred to as muddy water, can also reduce efficacy by interfering with the chemical reactions that produce the hydrogen peroxide.