Keep Mold, Mildew, & Fungus Out of Your Cannabis Garden

    Posted by Diane Campbell on Jan 2, 2016 9:30:00 AM


    Mold, mildew, or fungus can quickly devastate a cannabis crop. Avoid this heartbreaking experience by taking steps early to keep these organisms out of your garden, observing your plants closely throughout their lives, and acting quickly to address any problems that arise.



    Maintaining an environment that is less inviting to harmful plant diseases is much easier and more effective that treating your plants after disease has set in. Take these steps to resist mold, mildew, and fungus from the start.

    • Clean your pots, tools, and grow room thoroughly before you begin.
    • Keep humidity levels at or below 50%.
    • Keep temperatures between 70°-85° F.
    • Maintain good ventilation. Air should circulate around all parts of your plants; add fans to your grow room and prune densely-growing leaves as necessary to accomplish this.
    • In soil gardens, make sure soil is sufficiently aerated with perlite or similar components. In hydro gardens, use an air pump in the reservoir, and seal light out of it.
    • Make sure to dispose of any diseased plant tissue appropriately: seal in a plastic bag, and remove promptly from the grow room to prevent disease from spreading. NEVER leave old leaves to rot in the garbage in your grow room!


    Spotting & Treating Infected Plants

    Powdery Mildew

    Powdery mildew is a common problem in cannabis gardens, both indoors and outdoors. Catching this condition early gives you a great chance of beating it. It begins as small white spots on leaves that look like a fine dusting of powder. You may also see these spots on stems and buds. First, if you’re growing indoors, make sure your grow room’s temperature and humidity levels are appropriate (see above). Then, quickly take one of these steps:

    • Spray affected areas with a solution of 2 tsp baking soda per gallon of water. (Make sure to spray early in the light cycle to give the plants time to dry before the dark period.)
    • Spray with a solution of 1 Tbs hydrogen peroxide per gallon of water. (These two methods can be alternated for more effective control.)
    • If the infection is advanced, you may want to step up to a commercial product such as Serenade, which uses beneficial bacteria that combat a wide range of diseases and can be applied right up to harvest.


    Gray Mold (“Bud Rot”)

    Gray mold, known to marijuana growers as “bud rot” due to its tendency to infect lovely, fat colas from the inside and begin to turn them into disgusting slime, often before the grower even notices there is a problem. Bud rot can destroy a harvest in a matter of days, so quick action is critical. You might first notice gray areas circling your plant’s stems and yellowing leaves. The organism will move from the stem into the moist buds and begin to rot them from the inside. You may notice dead spots or a moldy appearance to the surface of your buds. If the disease is too far advanced, the plant will be useless as wells as an extreme hazard to the rest of your garden. Immediately take these steps:

    • Inspect every bud on the plant for signs of infection.
    • With clean tools and away from an uninfected plants, remove all infected tissue, and dispose of it in a sealed plastic bag.
    • If your plants are near maturity, consider harvesting early. Getting less than optimal THC levels is preferable to losing your harvest. Dry buds more quickly than you normally would, keeping temperatures above 70°F and air circulating around them.
    • If you attempt to continue your grow after removing infected tissue, treat with a biological spray such as Serenade. Most fungicides are unsafe to use late in flowering.


    Root Rot

    The first signs you see of root rot will likely be in the leaves of your plants, since they are more easily visible than the roots, and symptoms are easily confused with those of other problems, such as overwatering and nutrient deficiencies. That is because root rot smothers the plant’s roots, diminishing their ability to absorb oxygen, moisture, and nutrients. Symptoms of root rot may include:

    • Drooping, as though overwatered
    • Clawlike appearance to leaves
    • Yellowing or browning leaves
    • Decreased water consumption
    • Mildewy or rotting smell to soil

    If the problem is in its earliest stages, you may be able to correct it in one of two ways:

    • Use beneficial bacteria to prevent and treat root rot and make nutrients more available to the plant. Botanicare Hydroguard receives good reviews from cannabis growers for this purpose.
    • Water plants with a solution of 2 ½ tsp hydrogen peroxide per gallon of water. This will kill the organism that causes root rot while also delivering much needed oxygen to the roots. (At the same time, however, H2O2 will kill any beneficial bacteria in the soil.) Continue watering with this solution until plants have fully recovered.

    If root rot is more advanced, you will need to transplant your affected plants into new soil or other fresh hydroponic medium, cutting away slimy, dead roots in the process. Make sure to clean your tools with H2O2 or alcohol before you begin.


    Nature’s Gift Shop in Pueblo West wishes you success in your marijuana growing adventures! While you’re waiting for harvest, come in and check out our wide variety of lab-tested buds and other cannabis products. Click below to download our coupon, and get an extra half gram of any strain when you buy an eighth!

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    Topics: growing cannabis