Good Fungi vs. Bad Fungi in Indoor Gardening

Good Fungi vs. Bad Fungi in Indoor Gardening

Mold and mildew have given fungus a bad rep among indoor gardeners, and for good reason. Those are nasty blights that can make a mess of your crops and invite pests like fungus gnats into your growing room. There are even less welcome fungi, unseen types with unsavory names such as fusarium, pythium, and phytophthora. They can cause your plants or just the flower buds to rot and die. So what's the best way to stop a bad fungus? Arm your plants with an army of good fungi.

Your Heroes

Mycorrhizae (say it "my-core-rise-ah") are fungi that gather around the roots of plants. They help reinforce the cell walls on the outside of roots, making it harder for destructive fungi to colonize them. They also compete with the bad guys for food sources, starving the troublemakers for nutrients. These good fungi also keep open air pockets in the soil, which prevents bad fungi from spreading.


Cultivating the beneficial fungi is easy because you can buy them in powder, granular, and liquid form from your favorite indoor garden supplier. Sprinkle the powder onto plants' roots during transplanting, blend it into your soil mix, or simply dissolve it in the nutrient solution that you feed your plants. Start inoculating your plants with the fungi at the seedling stage because it can take a couple of weeks for them to get established. To ensure your plants are always protected by a healthy population of mycorrhizae, add a refresher dose every two to three weeks until you are about 14 days from harvest.


Mycorrhizae are not finicky, but they're at their most active when the temperature is 65 to 75 degrees F and the soil or solution pH is slightly acidic, 6.0 to 6.5. These good fungi thrive on natural fertilizers, especially those containing molasses or other sugars. An important function of mycorrhizae is extracting phosphorus for roots to take up. Excessive phosphates in chemical fertilizers tend to deactivate the fungi by making them unnecessary for extracting the nutrient.


Fungicides kill good as well as bad fungi. Even those that are compliant for use in organic gardening can wipe out your mycorrhizal army, while more toxic chemical treatments can render your soil or planting media uninhabitable for good fungi. So if you need to use fungicide to control problems in your indoor garden, use gentle products only and re-inoculate your plants with mycorrhizae after the problem is solved. Chemical herbicides and insecticides don't target fungi, but they can create conditions that are inhospitable for mycorrhizae. That's yet another good reason to use only products that are compliant for use in organic production.


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