If you want to successfully combat algae in your garden pond, one of the best methods is to deprive the algae of elements that they need to survive, such as light and nutrients. You can also introduce animals that like to feast on algae, such as fish or snails. It is of course possible to use poison instead, but poison is often dangerous for desirable organisms as well and is not a long-term solution. You should also keep in mind that a sudden mass-death caused by algacides can make the oxygen levels drop dangerously low in the water.
In many cases, you will see a significant improvement even if you can’t follow all the suggestions in this blog post. Pick a handful of them and try to see which ones that works best for your particular garden. Algae control in garden ponds need to be adjusted to each garden and gardener; there is no cure-all method suitable for all possible situations.
Limiting access to nutrients
- Use live plants in the pond. Live plants will compete with algae for the same nutrients and thriving plants will therefore make the environment less suitable for algae. Excessive algae growth in garden ponds is often the result of gardeners wishing to keep a fish-only pond or similar without any live plants.
- Avoid using phosphorous-rich fertilizers around the pond. Nutrients such as carbon and nitrogen is normally readily available in ponds, but finding enough phosphorous to sustain mass growth can be hard fort the algae unless phosphorous is added to the pond from the surrounding environment, e.g. through common garden fertilizers.
- Rainwater can easily transport nutrients from other parts of the garden to the pond. When creating a new pond, ideally avoid low regions of the garden to which rain water will run. If you wish to create a pond in a low area or if you already have a pond, you can build a protective embankment or similar around it. Planting flowers or other plants on and around the embankment is a good idea, because they will help absorb water and nutrients. You should however keep in mind that leaves and other types of organic litter that enters the pond from surrounding vegetation will provide the algae with nutrients.
- A buffer strip consisting of shrubs or high grasses can be created around the pond to make less water and nutrients reach the pond. In some gardens, the buffer strip does not have to go all the way around; it might be enough to create a buffer strip on one side of the pond (depending on elevation).
- Redirect run-off by digging diversion trenches.
Limiting access to light
- Include live plants in your garden pond. Live plants will compete with algae for light and make the water more shaded.
- When you dig a new pond, try to choose a protected spot or a spot where some type of protection can be arranged. Digging a pond directly under a tree is however rarely a good idea, because all the organic litter from the tree will bring nutrients to the pond which can boost algae growth.
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William Berg is an expert on aquarium and pond maintenance. He has among other things written the algae control section at aquaticcommunity.com.
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