How to Grow Blue-Green Algae in a Water Garden

What You'll Need
Large container or pond with light colored liner
Source of nutrients: nitrogen or phosphorus
Sunlit location
Warm temperatures
Pool skimmer to lift off built-up algae

Cyanobacteria, or blue-green algae, are a very primitive life form that creates food for many levels of nature's food chain. Growing blue-green algae in your water garden will attract aquatic wildlife and will add vivid color to your water garden environment. Follow these tips for growing blue-green algae successfully.

Warning: Blue-green algae can be toxic to animals, especially dogs.

Step 1 - Establish Your Water Garden

Place your water garden container or pond in a location where it will get more than 6 hours of sunlight per day. Make sure it has a light-colored skin or base inside, as this encourages algae to form by reflecting sunlight from the bottom of the water garden. Keep the water stagnant, as calm, warm water promotes the growth of blue-green algae.

Step 2 - Provide Nutrients

To start the growth of blue-green algae, add some storm water to your pond from a nearby lake or stream. This churned water, full of particles, has plenty of nutrients for the blue-green algae to feed on, such as phosphorus and nitrogen. The algae will provide food for zooplankton, microscopic aquatic animals that are the primary food for small fish.

Step 3 - Keep the Water Warm

Blue-green algae grow best in water above 70 degrees F (21 C). If your area has warm days but cool nights, cover your water garden at night to retain the warm temperature of the water.

Step 4 - Harvest Algae Regularly

Remove some of the blue-green algae from the surface of your pond with a pool skimmer, to allow sunlight to reach the bottom. The blue-green algae produce oxygen during photosynthesis in the daytime and consume it at night during respiration, so they can quickly use up the oxygen in your water garden. If this happens, your other aquatic wildlife will perish. Place the recovered algae in your garden or compost and water it lightly right away. If you have very dry soil, the blue-green algae can help the soil bind together and retain water, making it more useful for growing plants of all kinds. Blue-green algae has also been shown to reduce saltiness and balance high alkalinity in soils used to grow rice.


Monitor the other life in your water garden, especially rooted bottom-growing plants. If they start to die, then your algae is taking up too much space in the water garden, and you will need to remove some daily to maintain a healthy habitat for aquatic life. Do not allow pets or farm animals to drink the water from your water garden. Most blue-green algae stockpile ingredients for a toxic substance in their cells and release it into the environment when they die. It will cause nausea, vomiting, and twitching. It can even cause neural damage to animals that will kill them within 1 or 2 days of ingesting the toxin. Keep small children away from the water garden as well, and discourage them from wading in the water garden or splashing the water on themselves.