The use of barley straw to keep ponds clean is a practice that dates back to the Middle Ages. Barley prevents the growth of algae that leaves the pond water murky and devoid of the nutrients that fish and aquatic plants need to survive. Barley straw is also recommended by the Institute for Arable Crops Research in England as an effective algae control method. Barley straw works by releasing enzymes and humic acid as it decays that make the pond water an inhospitable environment for algae. Barley straw enzymes, however, are harmless to plants and fish. There are two primary methods for keeping a pond clean using barley straw. One will allow you to keep your straw treatment invisible while the other allows for a larger bag of straw and thus a more effective treatment.
Fill a small mesh or burlap bag loosely with barley straw. It is vital that the bag is made of a breathable material that will allow water to pass through the straw.
Place the bag of barley straw inside of a pond filter or water feature, such as a waterfall or fountain. This will allow water to continually pass through the straw and re-enter the pond while effectively hiding the barley straw bag. The straw is most effective when exposed to a source of running water that will oxygenate the straw, speed up the process of decay and carry enzymes and humic acid directly to the water.
Leave the barley straw bag in the filter or water feature. Replace the bag of straw after several months or if it begins to smell.
Fill a moderate size mesh or burlap bag with loosely packed barley straw.
Place a flotation device into the bag with the straw. Any floating bath toy or an empty water bottle will sufficiently keep the bag of straw floating on the surface. Barley straw will sink if not provided with a flotation device. Sunken straw that decays on the bottom of the pond will provide the pond with no benefits.
Use fishing line to tie the bag to either a weight on the edge of the pond or to an aeration device or water feature. The goal is to keep the bag of straw exposed to as much circulating water as possible.
Replace the bag of barley straw periodically as it decays.
Start barley straw treatments before you have an algae problem. Barley straw can prevent algae, but it cannot kill algae that is already there.
Do not use free floating barley straw or barley pellets. These will sink to the bottom of your pond and exacerbate the problem of a dirty pond rather than alleviate it.