Hi Penny,
By Sue Speichert
Originally published in Water Gardening Magazine, March/April 1999 Reprinted with permission.
Aquarticles
As the story goes, one warm and sunny summer day, a bale of barley straw fell into a farmer's pond in Scotland. He wasn't particularly worried about the straw in the pond and simply left it there. Several weeks later, the farmer noticed that there was less string algae in the pond than usual. The farmer's haphazard discovery made its way to the Centre for Aquatic Plant Management in England. The Centre undertook studies to investigate whether the presence of barley straw in water could affect string algae and blue-green algae. The studies confirm that barley straw does, in fact, stop the growth of all forms of algae. According to the Centre's published findings, barley straw is a"cheap and environmentally acceptable way of controlling algae in water bodies ranging from garden ponds to large reservoirs, streams, rivers and lakes."
In a nutshell, barley straw works by releasing a chemical that inhibits the growth of algae. It doesn't actually destroy algae that's already growing in the pond. Instead, it stops the algae before it has a chance to get started.
Barley straw works it magic as it breaks down and decomposes in the pond. It's a gradual process that's very temperature dependent, accelerating as the water warms. Once the straw becomes effective, it continues to inhibit algae growth until the straw is almost completely decomposed. As a general rule, the straw lasts for about six months.
According to the Centre, the precise way in which barley straw stops algae growth is "not fully proven." The Centre believes that when the straw rots, lignins in the cell walls are released into the water. The lignins oxidize into humic acids and other humic substances. When combined with sunlight and dissolved oxygen, these humic substances convert to hydrogen peroxide. Low levels of hydrogen peroxide have been proven to inhibit algae growth. Peroxides only last a few minutes; you would need a constant flow of fresh hydrogen peroxide into your pond water in order to keep algae at bay. When there's decomposing barley straw in the water, the peroxides are continuously produced (given sufficient sunlight and oxygen), and so the algae continuously inhibited from growing.
It's not known why barley straw works better than other forms of straw to keep the pond free of algae. Yet studies have found that barley straw is significantly better at ridding the pond of string algae and blue green algae, forms that beneficial bacteria is unable to keep at bay.
Barley straw only works if it is put in the pond before the algae begins to grow. It will not remove algae that is already present. Once the algae appears, it has to be removed by other means for the barley straw to go to work. This means manual removal of the algae or the use of some type of algaecide. Once the algae has been removed, though, the barley straw will be able to keep the algae from returning.
When determining how much barley straw to use, the important consideration is your surface area of water, not your water volume. The Centre recommends, as a general rule, that pond owners use about .03 ounces of straw for every square yard of water surface. If you've always had a lot of string algae, then you can use more. Once the algae is under control, you can scale back as you gain more experience with barley straw's effectiveness in your pond.
The best way to use barley straw in a backyard pond is to bundle it in a loose bag or nylon stocking. You can attach a string with a weight to keep the bundle from floating all over the pond. Remember, though, that as the straw becomes wet and waterlogged, it will sink to the bottom of the pond. It's important to keep the straw near the surface, because that's where there is more oxygen and also where the straw will have its greatest effect. Attach a cork or a plastic soda bottle to the bundle to keep it afloat.
In large, natural bodies of water, whether ponds, lakes, or streams, the straw should be loosely bundled in onion or potato sacks. It's better to use several smaller bundles rather than one large sack. Place the bundles at intervals so that the most amount of water surface is exposed to the straw's useful effects. In lakes, reservoirs, and ponds, the bundles should be held in place with a weight and kept from sinking by use of a float device. For streams, the bundles can be held in place at the shore and let to float out into the water, again using a float device to keep the bundles from sinking to the bottom.
In a backyard pond, one or two bundles will probably be sufficient. If there is no moving water, the bundle should be positioned in the middle of the pond, so that the anti-algae chemicals are able to disburse outward in all directions. If there is a stream or waterfall, then the bundle should be placed nearby, to take advantage of the increased oxygen and the additional dispersion of anti-algae chemicals throughout the entire pond. A header pool is an ideal location for a bundle of barley straw in a backyard garden pond.
It's best to put the barley straw into the pond early in the spring, so that it will have a chance to break down somewhat before algae would appear. The warmer your climate, the sooner you should place the barley straw in the pond. In mild or cool climates, February or March would be optimal. As a very general rule, it will take up to a month for the straw to become effective. When the water temperature is 70 F or warmer, the straw may take only a month to spring into action. If the water is cooler than 60 F, it can take up to 8 to 10 weeks for the straw to go into effect. Don't put in fresh bundles of barley straw during periods of prolonged hot weather – decaying straw combined with dying algae may deplete the amount of oxygen in the water.
If you live in a warmer climate where algae can be a problem even in the fall and winter, it's wise to place a new bundle in the pond in the fall before the old batch has completely rotted away. This will allow the new straw to become effective by the time the old straw needs to be thrown out.
As a general rule, new straw should be added every six months. This is just an average, however, and it's best to keep a close watch on whether new algae appears to be taking hold in the pond. Don't wait until all the straw is gone to add a new bundle. Add the new one while the old bundle is still working, so that there is an overlap. That way, the new straw will already be activated in the pond once the old bale of straw should be removed.
You can use straw in combination with algicides, either applying them when the straw is already in the pond, or using the algicide first and then waiting a while before adding the straw. The sooner you put the barley straw into the pond, the sooner it will inhibit the algae's return.
The Centre's studies have found that barley straw has no an adverse effect on aquatic plants or wildlife. In some cases, submerged plants have been able to grow better once straw was applied, most likely because the absence of algae allows for greater penetration of sunlight and facilitates photosynthesis in the plants. Straw has had no adverse effect on invertebrates such as Water Shrimp (Gammarus spp.) which eat waste and debris. They have been found to grow well and rapidly in the protected environment of the straw. Many invertebrates are in fact a benefit to the pond, since they eat decomposing organic matter, and some eat algae. As the straw decomposes and the number of invertebrates increases, they float way from the safety of the straw bales and are consumed by fish or birds, enriching the food source of these larger pond-lovers. Their numbers also increase and health improves from the presence of the barley straw. Again this is likely because the lack of algae allows for an increase in plant life and small animal life in the pond, which is an important food source for the fish and birds.
Maybe it just needs some fresh straw to clear it up a bit.