In England, barley straw has been used to manage algae blooms in reservoirs and other large bodies of water since the early 1990s, and more recently, homeowners have also discovered this nontoxic method of reducing pond algae. Although it has shown mixed results in laboratory tests, it is a popular garden and pond center product, with many loyal fans. Barley straw is available in a variety of formulations.
How It Works
Rather than killing algae, barley straw seems to prevent its growth, an effect Purdue University researchers refer to as “algistatic... rather than algicidal.” According to Purdue, research into barley straw’s ability to reduce algae growth suggests that “barley straw may reduce phosphorus concentrations which in turn reduce phytoplankton growth… observations suggest that (mat-forming algae's) growth was reduced (but not eliminated).”
The EPA defines a pesticide as "any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest." Because barley straw is not an EPA-registered pesticide, garden center and pond supply stores cannot sell it as an algae control product, but its use as a pond additive is safe and beneficial for fish and aquatic plants.
Barley Straw Bales
Barley straw is available in a variety of forms. It can be purchased in bales, bags, pillows and pads that are submerged or floated in a pond. Hiding and submerging straw bales takes some creative effort, but floating barley straw islands can be filled with ornamental plants and launched into the pond. Planters made of straw can be placed along the margins for bog plants.
Pellets and Extracts
Barley straw pellets and liquid extracts eliminate the need for dry straw completely. These forms often contain other beneficial pond additives, including enzymes and beneficial bacteria to help balance the pond and maintain water health. Pellets and extracts dissolve and become effective more quickly than loose straw.
When To Use
For best results, remove as much algae as possible from your pond before using barley straw. As part of your normal spring pond maintenance, scoop decaying leaves and debris, and remove algae-producing sludge. Barley straw bales should be placed in the pond during early spring, well before warm-weather algae blooms are expected to occur.
Although barley straw is not harmful to fish—in fact, it provides a welcome food source for them—too much barley straw can reduce oxygen levels in your pond as it begins to decay. The recommended application is .5 to 1.5 oz. of barley straw per 10 square feet of surface area. Bales should be removed at the end of the season to reduce organic decomposition and sludge.