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Grow Q&A: Why Is My Pot Growing Medium Turning Green?

Dear Dan,
I’m using coco as my medium to grow in, but I’m noticing the top layer of the mix is going green. Is that something I should be worried about and how can I stop it? — Nathan

Dear Nathan,
The surface of your growing medium is green because it is covered in algae. This fungus grows where water meets light and can cause you problems with your plant (besides just being gross and ugly to look at). Cover your growing medium with something waterproof and opaque—white plastic is best as it helps reflect back some light onto your lower growth. If you keep the light from reaching the wet medium, you will rid yourself of your algae issues.

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Don’t miss our previous Grow Q&A: Can I Flower My Pot Plants with Fluorescent Lights?

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Written By

Danny Danko is a writer, photographer and the Senior Cultivation Editor of High Times magazine. He has selected High Times’ annual Top 10 Strains of the Year since 2005 and is also the creator and founder of the High Times Seed Bank Hall of Fame, author of The Official High Times Field Guide to Marijuana Strains and the forthcoming book Cannabis: A Beginner's Guide to Growing Marijuana. He hosts the podcast High Times presents "Free Weed from Danny Danko."



  1. Avatar

    Kenshin Himura

    September 5, 2016 at 8:40 am

    You’re keeping your shit too wet for too long if it’s turning green. Learn 2 grow.

    • Avatar

      Bruce McCluskey

      September 5, 2016 at 8:08 pm

      easy bro not all are masters

  2. Avatar

    Pamel Greg

    September 5, 2016 at 2:43 pm

    #420 for life

  3. Avatar


    September 5, 2016 at 5:11 pm

    Algae isn’t fungus. It is a chlorophyll producing PLANT. Jeez!

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