White mold on coco coir? (not on plants) How concerned should I be?

Hello New Friends,

I’m growing for the first time following the guide here, https://www.growweedeasy.com/250w-hps-beginner-tutorial, but I bought my seeds here from ILGM. Only difference from the guide is that I’m using a 48x36x80 tent and a 400w HPS turned down to 75%.

On to the problem.

I’m seeing what looks like a fuzzy white mold growing around the edges of the pot on the coco coir itself. I’m fairly certain it’s not salt. Nothing on or in the immediate area of the plants, and they appear to be healthy at this point, 1 week and 1 day above ground. How concerned should I be about this?

I’m considering getting some Plant Protector, specifically for the Mold Control from this site and applying as directed, but I’m not even sure that will address this issue.

Can anyone help identify this issue, tell me how concerned I should be, and possibly provide tips to resolve if it is in fact a problem?


And to head off related questions, here is the nutrient schedule. https://www.growweedeasy.com/wp-content/uploads/2016/08/Auto-Flowering-Coco-Coir-Nutrients-Flora-Series-Trio-CaliMagic.pdf

Also, the plant on the bottom right was planted later than the others, which is why she’s smaller.

Alright. No answers here yet but after further research I’ve come across this video which appears to address a similar problem. https://youtu.be/zbFvv06Ip5g

It recommends spraying a hydrogen peroxide/water mix on the affected areas. Does anyone know of a reason why I SHOULD NOT try this?

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Other than having to re introduce your microbes no probs.
The H2o2 will kill them off. :+1::v:


I don’t think what your seeing will harm anything. Sometimes “mold is gold” if it were me I would welcome living things doing their thing.

I have something that looks similar growing in my spinach pot and it’s growing on the BTi granules I sprinkled on the top soil and I’m not worried


Thanks for the responses.

For anyone else who runs into this, I came across this other video which indicates that this particular mold is not harmful (though the narrator’s voice might be): https://www.youtube.com/watch?v=uaRtzuuYYdE

Through additional research, it also seems to be a result of too much moisture sitting on the surface of the coir. Ultimately, I think I had insufficient airflow in my tent, which is supported by one of my babies falling over despite appearing otherwise healthy. On closer inspection, it was getting little to no airflow compared to the other three, and I’ve been reading about how important direct airflow can be for promoting a strong stem.

So I’ve added 2 more fans to the tent and readjusted for more direct airflow (not too much), and am going to change watering habits to less quantity, more frequency waterings. Going to try this before attempting to spray with peroxide mixture.

I’ll let yall know how it goes.


I’m with you; the seedling is extremely resistant to white powdery mildew and at this point you would like to build a ‘soil’ ecology to help the plant metabolize nutrients. In fact it’s not a bad idea to put some mycorrhizai on the top soil layer of your media.


Good to know. Thank you all for helping calm my fear. Other than the one that fell over (which appears to be doing a bit better today) they seem to be quite healthy, so I didn’t want this creeping mold to sabotage my crop later on.

Hopefully this thread is useful to someone else who sees this.

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I found a similar mold on the top of my coco coir still in an already opened bag. When the garage door was open, it got the full sun, so the moisture that collected in the top of the clipped bag helped this mold to flourish in the warm and dark environment. It was only on the surface… so, I just mixed it up with the rest of the soil, bone meal and vermiculite to use for transplanting the two 4-week old plants in the grow tent.
So far, so good. I also sprinkled some cinnamon on the soil around the stems to reduce any fungus or mold from getting a start there.
I’m confident that this won’t have a negative effect on the plants.

Actually, i separately had the same situation you’ve just described with some kind of fungus (was actually a little yellowish) living in an opened bag of coir that got some sun.

At this point I’ve had 2 harvests, total 8 plants that at one point or another exhibited the (white) mold on top of the coir and i can say there are no ill effects. Plants grew and thrived, harvested, dried and smoked just fine.

I’m mid-flower with the coir that had the yellow fungus in it, and there have been no visible issues so far. Things seem to be fine.