Although typically low maintenance, the humid conditions in a rain barrel allow algae to thrive. Not only can too much algae clog your outlet hose and overflow valve, the waste products of a vigorous algae bloom can also harm your plants. Taking a little extra care with the placement and conditions of your rain barrel will help prevent excessive algal growth.
Whenever possible, place your rain barrels where they will be out of direct sunlight. If you prefer, you can direct your downspouts around the corner of your house. Like other plants, algae needs sunlight to grow and spread. By keeping your barrels on the side of your home that receives the least amount of sun, you can curb algal growth. This will slow its ability to reproduce and take over the inside of the barrel.
Barrels in the Sun
Unless you are doing a major remodel or having a new home built, you often can't control where your downspouts are located. If you can't help but have a barrel in the sun, opt for a barrel made of opaque plastic so the walls of the barrel shade the water inside. If you're making a rain barrel yourself and only have access to transparent or white plastic barrels, paint the barrels to block out sunlight. If you match this coat of paint to your house's exterior color, you can add to the visual appeal of your rain barrel system. Another method to keep the sun from hitting your barrel is to build a screen around it. If you choose to use a screen, place it in such a way that you can access the barrel for maintenance and water use.
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Clean Your Gutters
Algae not only need sunlight to grow, but it also needs nutrients. If your gutters are filled with leaves or conifer needles, rain water soaks the debris and leaches nutrients from it. These nutrients then wash into your rain barrel where they provide a healthy meal for algae. Keeping your gutters free of leaves and debris will cut off this nutrient supply and limit algal growth.
Once algae gets a foothold in your barrel, it will continue to grow. The best way to control algae is to clean your rain barrels once a year. This annual cleaning is best done in the summer after you've used the water in the barrels. In barrels where there is no algae present, you can simply hose out the inside of the barrel with a strong jet of water. If you do notice algae, rinse the barrel with a solution of three-quarters cup bleach to one gallon of water, and then scrub out the algae. Rinse the barrel well and let it air dry for 24 hours to clear out the chlorine before reinstalling the barrel.