With the rise in popularity of ponds and water gardens came the demand for simple methods of pond algae control to prevent scum algae and stringy algae from taking over the pond. There are several chemical methods of control, but one of the more popular methods of control involves using Barley straw as a natural preventative. Long used in Europe, the Barley bales have become much more prevalent in the pond keeping hobby.
The Barley straw usually comes as a woven mat or a tightly bound bale, perhaps in a mesh netting that is placed submerged in the pond. You may need to anchor it with a small rock or tie off, but you do not want to block too much of the surface of the Barley. It is best to place the barley in the pond before the algae gets out of control. It can prevent new growth but usually has no effect on algae already present. Once submersed, it will take 3 to 4 weeks for the Barley to become effective. There is a fungus that grows on the barley that actually produces the chemicals which inhibit the new growth of algae. The structure of the barley also provides a protected surface for the growth of other beneficial micro-organism that will compete with the nuisance algae for available food (phosphate and nitrate).
You will want to place the Barley in an area with some water flow to make sure there is plenty of oxygenated water passing through the Barley to promote the growth of the fungus and microplankton. While most bales give a size estimate for the volume of water they treat, generically, you would use 1 ounce of straw for every 10 square feet of surface. For those of you with really large systems, that works out to a 225 pound bale for one acre of surface area! The Barley is pretty much used up after 6 months in the pond and should be replaced at that time. It is best to add the new bale about one month before removing the old bale.
Manufacturers make concentrated liquid or pelleted forms of the Barley straw that might be easier to place in filter systems, but will probably need to be replaced after 3 to 4 months. The liquid concentrates need to be added every week for a month, then once a month to be effective. You will not see Barley sold as an “algae control” because FDA regulations would then label the Barley a pesticide and entail multiple licenses and additional costs. Barley is considered a home remedy instead. Used properly, the barley can restrict the growth of scum, floating algae and stringy hair algae attached to rocks. It is a valuable weapon in the hobbyist’s arsenal to eliminate algae.