Organically Control Mosquitoes and Algae in Rain Barrels

The standing water in rain barrels is the ideal breeding ground for disease carrying mosquitoes. I don't know how, but mosquitoes bred in my friend's rain barrels even though she kept a lid on them. 

No Work Solutions

There are two no work solutions for keeping mosquitoes out of our rain barrels: vegetable oil or dish soap. Both create a film on the water that will prevent the mosquito larvae from getting oxygen, thus drowning them. After each rain, add 1/4 cup of either to your rain barrel. I don't use this option because I don't want to add vegetable oil or soap to my garden soil. 

Sustainable Gardening Solution: Goldfish

I keep mosquitoes out of my rain barrels and actually decrease the mosquito population neighborhood-wide by keeping goldfish in my rain barrels. Yes, the super cheap 10/$2 goldifsh.

Now I have read some ridiculous things about how to keep goldfish. Everything from "they need heaters" to "they need air pumps". Not true at all. Goldfish are very hardy and require very little maintenance. Per 30 gallon rain barrel I keep 3 goldfish - no heater, no pump. 

Goldfish Maintenance Requirements

Goldfish just don't need a heater. Mine lasted and are healthy after overwintering. Keep in mind that we do live in North Texas, so they were only under 1/2" - 1" of ice for a few days, but the weather did stay down in the 30's-40's. 

They also don't need an air pump. Wind across the water and water plants provide plenty of oxygen for the fish. Plus if for any reason the oxygen levels get low, goldfish will swim to the surface and suck air down into the water. If you see your fish doing this, you need to add a water plant. 

There are quite a few water plant options. The plant's roots add oxygen to the water, and the fish's poop feeds the plant. The plant also provides shade in the heat and protection from predators. A filter system is unnecessary to remove ammonia build up from the fish poop as the plant's eat the "liquid fertilizer".

I have an overabundance of spider plants so I gently pull a few up and float them in a wire basket, letting their roots dangle in the water. Spider plants aren't a water plant, but thrive just fine in this set up. I haven't tried it yet, but small scale hydroponics is an option for rain barrels.

Feeding Your Fish

I have fed my goldfish two ways. The first was just grabbing a thing goldfish crisps when I bought the fish. You feed them twice a day about 2 crisps per inch of fish. I have 3 fish per barrel that are each about 2" long, so I toss in 12 crisps per barrel twice a day. I do this in the morning when I wake up and then at lunch time. I don't feed them an evening meal because evening is when mosquitoes are most active and will come to lay their eggs. 

Now that my garden is established, I feed my goldfish chia seeds. (Post about how to grow your own chia for seeds coming soon.) Chia seeds are packed with nutrients and protein. It doesn't take many chia seeds to feed goldifsh, so I add about 1/4 tsp per rain barrel twice a day to feed 3 fish. 

Other Types of Fish

I have also tried keeping breeder guppies in rain barrels. They reproduce quickly, so I estimate we went through 5 generations in a season. However, the poor guys weren't as hardy as the goldfish and succumbed to winter weather. I'm an animal lover and hated seeing this happen, but the "who survives winter" experiment was necessary. The circle of life goes on and they are fertilizing my spring garden. 

Controlling Algae in Rain Barrels

As a side note, goldfish also keep algae from forming in the rain barrels by munching on it. Keeping plants in your rain barrels also inhibits algae growth by shading the water, thus blocking the light algae needs to grow. Established plants will also take up the nutrients from the water before the algae has a chance.

For more about rain barrel options and what you need to know about installing rain barrels, see my post Rain Barrel Options and Installation.



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