Reduce Nutrients
Algae is a plant that has no roots. It has to take its nutrients directly from the water. This means it can grow very fast when food is present, but it is also possible to starve it by reducing the amount of nitrates and phosphates in the water.
The two most common sources in garden ponds are rotting vegetation and tap water. Unfortunately our tap water in the U.K has high levels of phosphate fertiliser in most areas; this is not harmful to humans but makes algae grow very fast! Other possibilities are excessive fish or duck feeding, or runoff of fertiliser from surrounding fields or lawns.
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Try to use rainwater only to top up a pond. Fix any leaks so you do not have to refill as often and consider adding water butts or rain storage tanks if you have space. It is suprising how much the average house roof can collect! Use a net to cover the water if it is near trees that drop leaves in the Winter.
Schedule an annual pond clean up where you remove as much dead and dying vegetation from the water and margins as possible. Autumn and early Winter is the time that you will cause the least disturbance to wildlife.
Pile everything you gather up next to the pond for 24 hrs to give a chance for any creatures to escape.
This is a good time to remove plants if you have too many - these can be composted. Do not add compost or garden soil when planting pond plants, use aquatic compost only. Be very careful when applying fertiliser near water.
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Or.. Why does my pond turn GREEN! Why would putting straw in it help? Would using chemicals be more effective?
Controlling Filamentous Algae
Algae are tiny floating plants that live in water. They can be 'planktonic' meaning they float around on their own - this will cause water to look like pea soup. They can also be 'filamentous' meaning the cells join together to form long strings. This is often the type that causes the most upset to pond owners because it is unsightly and can block pumps and filters and suffocate plants.
Chemical treatments do not just kill algae - they will also destroy beneficial microorganisms that can have a long term effect on the health of plants and fish. Use of barley straw will promote a more sustainable and healthy pond.
Barley straw is organic and harmless to pets and wildlife. When it rots it will produce humic acid, which is turned into a trace amount of hydrogen peroxide by the sun, which will not harm fish or aquatic plants but will stop algae like blanketweed developing properly. This process is called allelopathy.
Algae will first stop growing, then turn yellow and die. Barley straw works best when used early in the season and regularly, and used with other good pond management techniques. These are:
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Reduce Sunlight
Algae needs sun to grow, so reducing the amount of light the water receives in Summer is important. Use aquatic plants like Rigid hornwort (Ceratophyllum demersum) if you have a smaller pond, and water lillies like Nymphaea alba if you have a large one to shade the surface. Aim for around 50% surface coverage in Summer. These are both U.K native plants which will not cause problems if they escape into streams or rivers. You can also use Canadian pondweed (Elodea canadensis); this is fast growing and easy to buy, but be careful where you dispose of it! This will also help to slow evaporation, and they will compete with the algae for nutrients.
Increase Oxygen
When the water has more oxygen it wil encourage the growth of aerobic bacteria - these consume the same food as algae, so will help to slow growth.
You can also use a fountain, aerating pump, waterfall or solar powered rotating paddles to stir up the water. Be creative! It is a great excuse for a water feature.
If you see bubbles, it is helping.
The beneficial bacteria present in Barley Bag helps to kickstart this process will rapidly multiply in the pond to help clean water of black sludge and pollutants, improving water clarity and reducing foul odours and ammonia. You should have natural bacteria present, but the process might take a little longer.
