White Mold Growing On My Potting Soil?
So do I use it or lose it?
A few weeks ago, I opened the door on my garden shed and found something looking like snow drifts on the surface of my potting soil! Truly, it was white mold on my potting soil!
I store my potting soil in an old soak sink that my son discarded. And I sometimes keep an old vinyl tablecloth over the top of the soil. I do this because I forget to close the door of the shed sometimes (even overnight), and I don’t want it to become the local “outhouse” for the cats or other animals who may visit in the night.
It seems that the combination of soil and warmth and a little condensation from the soil sink being covered with a vinyl sheet, I had created a perfect environment for the mold to grow. My garden shed gets really hot through the day and then cools considerably in the nights. Here comes condensation.
Furry and white mold is called mycelium
Mushrooms, along with yeasts and mold, are examples of fungi. Mold is a type of fungus and is important in soil because it helps to break down the components of the soil into the nutrients which then are available for the plant’s roots to take nutrients in to the plant.
You see, soil is teeming with life, and most of the time it is invisible to the naked eye.
But the fungi in the soil is part of the web that makes up the living organism network and results in our plants thriving in this fertile soil.
You might find some white mold on the surface of a plant’s soil in a container, but that may be due to too much moisture. Soil bagged for sale may have mold in it when it is opened, but that would be due to moisture and darkness inside that bag.
Exposure to light would have the mold retreating back below the surface again.
I fixed the situation by pulling off the vinyl cover and exposing the soil to the air. I left the door open to the garden shed and just thought I could keep an eye on it in case cats, birds, wasp ( those are one of the little varmints who come looking to make a nest.)
In a few days, it was almost all gone and the soil looked wonderful. In fact, I felt so confident in what I had read, I planted up my terrariums here.
If there is mold in a potted plant, just break up the soil to be sure it hasn’t created any water dam. If you like, you can replace it with new soil if it bothers you.
But I am comfortable with my soil and I plan to not let it develop such a humid/moist environment in the future.
If you buy soil and it has white fuzzy mold, that shows it is alive and doing well. Just let it get some sun and air and you are gold!
I got new soil and plants from a local store. After a week I started noticing fungi growing on all the new plants’ soil. The fungi resides on top of the soil and not the plants. I have decided to space the watering more on all of them, but in the meantime I am not sure if I need to do anything to avoid affecting the plants
I would let it dry out more between watering and perhaps sprinkle a bit of cinnamon and mix it into soil. Just a dash or two.
This is super helpful! Thanks so much
Thanks – you stopped me from throwing out a nearly new bag of potting compost 🙂
I have a beautiful peace lily that is 4 years old. I have repotted it once and do not over water it. It is sitting in my sun room where it gets filtered bright light all day long. It continues to bloom and thrive. When checking it today, I see a white substance on the top of the soil all the way around the plant. It isn’t too wet, it feels dry to me. I routinely clip off the yellow leaves. I just want to know if I should scrape this off the top or is it not dangerous to the plant? I plan on separating it soon in new soil. Any help is appreciated.
It seems that it would not be white mold since it is not too damp from your description. Perhaps it is just salinity in the water and it is accumulating on the top of the soil. Maybe removing those top few inches of soil and replacing with fresh soil might make it do better. Hopefully that helps.
Thank you so much for posting this useful information!
I had been replacing the soil in my window boxes every year for my petunias. This year I was pressed for time so I left it and just added leaf mulch and petunia fertilizer. That was six weeks ago and my petunias are bursting with flowers and overflowing the boxes. I think I will try to get away with it again next year.
Sounds like you are the Petunia Whisperer this year. I don’t have good luck with petunias. Happy for you!
Thank you so much for this info now that I know what to do this will save me I really really thought it was my water I was using and drinking I was going crazy and I was going to have the water I buy tested lol I’m so glad I came a cross this
You are so welcome and thanks so much for taking the time to tell me so!
I was always dumping my soil out and buying new, a few years ago I was told I could reuse my soil from old plants. Is this a good idea? I have seen this white mold in the pots I have forgotten to empty in my storage shed. I usually discard the top layer and empty my pots in a big tub for later use. So thank you for this information.
You’re welcome. I have re-used potting soil a lot. Just adding some sprinkle of cinnamon and usually some new soil too in the mix. Works great for me. And I am not afraid of a little mold now that I have done the research.
Cinnamon, that’s interesting. What is the benefit or reason for adding it?
I have practiced adding a little cinnamon to my soil (especially when it has already been used, or like in this linked post, already seem to have some problems.) https://www.thehypertufagardener.com/cinnamon-use-for-plants/ It seems to help with fungus attacking the plant. Saved my Baby Tears from near death!