Where Is That Fungus Coming From?

Growing cannabis in New England is already challenging enough thanks to the unpredictable weather, but how are growing mediums contributing to moldy crops?

Cannabis cultivators know that growing in New England comes with its own host of issues. The weather can change in an instant, and any hope for controlling the humidity of your grow goes out the window with a few days of heavy rain. 

When your environmental conditions can’t be dialed in to perfection, a single spore landing in your colas means you might find yourself cracking open a bud to find that dreadful mold we all know and hate. What was once the frosty white promise of THCA rich trichomes becomes the webbed and fuzzy blight of a wasted crop cycle. But you were so careful! You sterilized the inside of your tent between crops and you always clean your pruners with isopropyl alcohol before working on your plants; so how did that spore get there in the first place? The answer might be your growing media. 

An article published in October 2019 by the Department of Biological Sciences at Simon Fraser University identified a broad range of fungal species in unopened and unused bags of commercially available coco coir growing media. The species detected ranged from aspergillus species (known to be potentially harmful to people with compromised immune systems) to fusarium species (responsible for the “damping off” of freshly germinated plant seedlings). Even bags of coco coir that had undergone sterilization were found to contain penicillium species (that fuzzy white mold growing inside your best looking cola). 

But coco coir is so affordable and you already bought a dozen bags! What can you do? With some careful planning and good practices, you can lower the risk of these spores germinating and contaminating your crop. As with any agricultural model, you will never be able to lower your risk of crop loss to zero, but there are steps you can take to protect your harvest. 

The leading cause of a mold outbreak on your coco coir surface is a combination of added sugars and overwatering. There are many carbohydrate products on the market, and while a bit of sugar in your root zone might give your young plants a quick boost, an excess of sugar can easily turn a happy root ball into a petri dish from hell. Like in nature, your cannabis plants will produce their own carbohydrate rich exudates to feed whatever beneficial microbes are in your root zone. Before dumping a spoonful of black strap molasses into your coco coir, consider, “do microbes in nature need this?”

Added sugars aside, your coco coir is still a pot full of the stuff mold craves. In order to keep mold at bay, careful water control is critical. The leading cause of death for all house-plants is overwatering, and while nobody wants to see their babies wilting, a proper dry back will enhance rooting and dramatically lower your risk of molding out. Keep a careful watch on the surface of your coco coir, and if you see anything fuzzy and filamentous starting to grow, go easy on the water! Sprinkling a bit more growth media or diatomaceous earth over the mold may act as a shield to prevent the bulk of spores from wafting through the air into your nugs. Always wash your hands between touching your pots and managing your plants, and if possible, wear gloves and change them often. Remember, all mold needs to grow is a food source and the right amount of available water. Controlling these factors to the best of your ability is your main defense against crop loss, so be diligent!