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What’s the newest, most innovative and cost effective way of controlling the simpler forms of algae in a water gardening setting?   Well, how about tossing a small bale of Barley Straw into the pond?  Yep,   we said “Barley Straw”.    Farmers in Scotland have used this method to control green floating algae in farm ponds for centuries (or so the story goes).  Nobody knew how or why it worked, but the farmers would toss in a couple bales of their straw every spring.  The United Kingdom’s IACR-Center for Aquatic Plant Management (formerly the Aquatic Weeds Research Unit) has conducted extensive testing into the dosage regimen and method of action for Barley Straw’s algaecidal reputation.

How Does it work?

When the Barley Straw is introduced into the pond, it soon begins to decay (decompose, rot).  Though not fully proven, it is suspected that the rotting straw releases lignins into the water.  In the presence of plenty of oxygen, the lignins are oxidized into humic acids and other humic substances.  It is also known that when sunlight penetrates water containing humic substances and dissolved oxygen, very small amounts of hydrogen peroxide are produced. Very low levels of hydrogen peroxide are known to prevent algae cells from reproducing and inhibit the growth of existing algae cells.

Since the barley straw releases it’s active ingredients while decaying slowly, there is a constant low dose supply of these algae inhibiting chemicals.  The existing algae cells are not killed outright, but since they no longer grow and cannot reproduce, the algae bloom will be controlled or prevented.

When Barley Straw is applied to a pond that is already pea soup green, it can take up to several months for all of the existing algae to die off and the water to become clear.  If added in the early spring, or in a new pond start-up, Barley Straw can prevent the algae from ever becoming established.

What Types of Algae Does it Work On?

Barley Straw works VERY effectively to control the planktonic floating green algae that makes our water look like pea soup.  Research indicates it can also be a valuable aid in controlling string algae.  It is most effective against string algae if applied before the stuff ever develops.  In our experience, it works wonders at keeping the water clear, but doesn’t work nearly so well against string algae.   But what the heck, you can’t ask for everything, can you?

Barley Straw has absolutely no detectable effect on any higher order plant or animal life.  In fact, some folks think their koi and goldfish are healthier because of improved water conditions and the presence of small invertebrates (read as fish food) in and around the straw bale.

Dosage.  How much to use and how often to use it? The single most important factor in determining dose is the surface area of the pond to be treated.  Depth does not appear to greatly affect dosage schedules.  This sort of makes sense when we remember that the sunlight penetration into the first couple inches of water is where the conversion to peroxide occurs, and that the surface layers is where most of the algae is.

The Center for Aquatic Plant Management recommends that “still” bodies of waters require a minimum of 10 grams of straw per square meter of surface area. This minimum dose roughly translates into about 1/3 ounce of straw per square yard of surface area.  Most commercial pond companies we’ve found offer 4 ounce bales.

Use common sense in modifying the dosage.  In water that is very heavily laden with algae, doses of 50-100 grams (roughly 2-4 ounces) per square meter may be required initially, then may be decreased once the algae is under control.  Higher doses are also indicated in very muddy or turbid waters.  In very large bodies of water, the straw bales should be dispersed evenly around the pond for better effect.

The rate of decomposition of the straw is very dependent on water temperatures and levels of dissolved oxygen.  In colder water, the straw may take up to 6-8 weeks to become effective.  Water temperatures over 75 degrees allows for faster microbial activity and the straw becomes effective in about 1-2 weeks.  While most folks can expect to get five or six months out of each bale of straw applied, we poor southern warm weather folks usually need to replace the decomposed bales every 3 months or so.  The algaecidal activity continues until the straw is completely decomposed (read as “gone”), but to maintain continuous coverage you need to start a new bale before the old one disappears.  We make sure there fresh bales of straw in all our ponds early in February to ensure they’ll become active by the time the spring algae bloom tries to occur.

How and Where is it Applied?

There are two varying schools of thought as to how best to use Barley Straw.  The initial researchers recommend that the straw be placed in loose bales or in net bags and positioned where there is strong movement of freshly oxygenated water.

In our experience, in smaller garden ponds that are 3 foot deep or less, it really doesn’t matter how you apply it.  Just chunk it in the pond.  You can use bales, tied sheaves, scattered loose straw, or the neat little net bags.  The straw can be put in most biofilters, floated in the pond, stuck up under the waterfall, or put in the middle of the pond weighted down with a rock.  As long as the pond has good healthy water flow and adequate aeration, it really doesn’t matter a lot how you use it.  In dirt bottom farm ponds, it may make a difference, but not in most water gardening situations.

Can I Use Other Types of Straw?

Folks who are trying to use non-barley types of straw report varying degrees of success.  Those with good results have used wheat and rice straw, but at significantly higher doses and with less dramatic results when compared to Barley Straw users.  If Barley Straw is absolutely out your reach, try to find straw from wheat, linseed, oil seed rape, lavender stalks, or maize.  It’s likely that you’ll have to use 5 times the dose or more and apply it more frequently, but it can work.

The Negative Side of the Reports

Some folks have reported that their ponds fill with small chunks of floating straw and that these clog the pump and/or filter. There was some straw escape from the first bundles we ordered too, though we didn’t see it as a problem.  To correct it, however, we sell our straw bales in a close knit (800 micron) net bag which holds the big stuff in.

Some folks have also said they saw no difference in their pond at all after adding barley straw.  In closer questioning, we’ve found most of them to fall into two groups, ones who had already clear ponds and those who applied too small of an amount for too little time to a pond already too far gone in algae due to “other” design or care elements.