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Some kind of white mold is infesting several of my plants, below is one of the worst infections of a tomato seedling. It is very aggressive, if I remove the top layer of soil it will come back in a single day. It has infected some basil seedlings as well.

It is mostly white, but forms slightly yellow centers in some places, as can be seen from the picture.

Can you identify what it is? And how do I get rid of it?

Click on photo for full size

White mold

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What kind of soil and fertilizer did you use? Did either of them have mycorrhizae included? – stormy Jul 23 '14 at 19:45

2 Answers 2

up vote 7 down vote accepted

There are many possible types of fungi or slime mould that this could be but the cause and treatment are the same.

The source is wood which is part of a soil mix that has been inadequately composted or sterilized. The culprit is eating the woody bits in the soil.

You cannot control this just by removing the soil as it will be found throughout the soil. There is no harm to people or a mature plant but seedlings might not like the competition.

Control measures include:

  • keep the soil drier. They need a moist or wet soil to thrive
  • I have read suggestions to sprinkle cinnamon on the soil but have no research to prove it
  • a copper based fungicide will probably do the job but it could kill the seedlings as well

Probably the best solution is to learn to live with it. Do not use any unused portions of that bag of soil unless you have sterilized in the oven at ~212 degrees Fahrenheit (= 100 degrees Celsius) for twenty minutes or so. Caution: the smell of baking soil will not be appreciated by everyone!

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Good points. I've seen these sometimes on those jiffy pots at retail operations after they've been there a bit. – itsmatt May 22 '13 at 11:56
Thank you. I will go for ventilating a lot, watering a bit less and keep removing any mold that forms on top. – Bjarke Freund-Hansen May 23 '13 at 5:48
Also trying the cinnamon now, I am hoping it does not affect the tomatoes. :) – Bjarke Freund-Hansen May 23 '13 at 19:44
Cinnamon is also a root hormone, stimulates quicker root system/growth & bug repellent. Dip the stem of your starts in it before planting. Won't hurt tomatoes, only help. – user6803 Jul 14 '14 at 14:40

(Peace Lily plant) I had the same white fuzzy mold on my soil for a few months before I noticed it. I repotted the plant with a new pot and tried to replace as much old dirt as I could. I sprinkled cinnamon all over the top soil and have observed for a few weeks. Where there were gaps in the cinnamon, the mold grew back, but very lightly. I scraped it away, added a little more soil and then put cinnamon all over the soil (like 99% covered). Finally, today I checked and the mold only grew in one small spot that was missed as well as on the end of a broken off branch. So cinnamon does definitely work, at least in this case. My soil drains well but remains too moist and the cinnamon really did the trick. However, it is too much of a hassle to always have it sprinkled on the soil, so I will probably just trash the plant and start with a new one.

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