How to Treat String Algae in Backyard Ponds

Many homeowners fear chemical solutions to algae that may kill pond life.

Filamentous algae seems to come out of nowhere, floating off the bottom of your backyard pond and filling it with stringy green goo. Uncontrolled string algae is more than an eyesore; it can kill fish and pond plants. Commerce offers myriad solutions to the problem ranging from the mechanical to the chemical, each with advantages and disadvantages. Europeans have used barley straw for years to control algae and it is gaining in popularity in the United States as it does not injure pond-life yet provides long-term algae control.

Things You'll Need

• Dried barley straw
• Mesh bag(s)
• Stones or bricks

Instructions

1. Measure or approximate the surface area of your pond by multiplying the diameter by 3.14. Calculate the amount of barley straw based on 0.025 pounds per square yard. Decomposing barley straw releases hydrogen peroxide which prevents algae development. Large ponds of one acre require 107 pounds of straw or two or three standard-sized bales, according to the Ohio State University Extension. Small ponds of 100 square feet need only 0.01 pounds of dried barley.

2. Place the correct amount of barley straw loosely into the mesh bag in April. If you are treating a large pond and require one or more bales of barley straw, break up each bale as much as possible before putting the straw in the bag or bags. Only barley straw that decomposed in the presence of oxygen produces the compound that inhibits algae; if the straw remains tightly baled, the center will decompose without oxygen and prove ineffective against string algae.

3. Add sufficient stones to each mesh bag to keep it at the bottom of the pond. In a large pond, sink the mesh bags around the perimeter of the pond in water no deeper than 6 feet.

4. Replace the straw with fresh straw in July if your pond has a history of algae problems.

Tips & Warnings

• Attach ropes to the bags before you put them in the water to make it easier to recover them.

• As the barley straw produces clear pond water, additional light infiltrates the pond. Pond weed and other plants may grow at an increased rate.

References

• Ohio State University Extension Fact Sheet: Algae Control with Barley Straw
• Doctors Foster and Smith Pet Education: Control Pond Algae with Light, Nutrient Control, Filtration, & Algaecides