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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Wednesday - January 12, 2011

From: Gilroy, CA
Region: California
Topic: Compost and Mulch, Diseases and Disorders
Title: Getting rid of algae on dirt and patio
Answered by: Nan Hampton

QUESTION:

Algae and on patio and dirt, and how to get rid of same?

ANSWER:

I'm guessing you meant to say "algae and (moss) on patio and dirt".  Am I right?  If you have either one in such a situation, you usually have both.  The reason they are growing there is that they are experiencing continuous moisture and very little sunshine.  Those are two of the major requirements for algae and moss to grow.  First, we will talk about your soil.  Poor drainage is very likely a major factor with soil that remains moist.  If your soil is very dense and compacted, aerating it and adding compost and/or mulch to it will improve its drainage.  The University of California Cooperative Extension Service has an article, "Moss and Algae Do Well in Wet Weather and Poorly Drained Soils", that offers other suggestions for eliminating algae and mosses which include applications of copper sulfate, ferrous sulfate or ferrous ammonium sulfate.  Another recommendation from the Yard Doctor: Central Northwest suggests using sodium hypochlorite (or copper sulfate) in a 1% or 2% solution to spray the area.

If you Google the terms "eliminating algae from patio", you will get lots of suggestions for removing algae from patio bricks which include power washing, dilute bleach solutions and algaecides.  Again, changing the elements that cause the problem (poor drainage and too much shade), are important in order to keep the algae from returning.  How you remove the algae depends on the size of the area, the intensity of its growth and what plants or structures are nearby that might be impacted by the treatment.  Here are a couple of sites that have suggestions:  from Desmesne and from the Royal Horticultural Society in the UK.  You can consult a reputable local nursery or home supply store to find the most effective and ecologically responsible algaecides.  I would also suggest you contact your Santa Clara office of the University of California Cooperative Extension Services for suggestions for removing the algae.

 

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