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On the edge of three of my flower pots is growing this white hairy layer after I returned from a two weeks vacation. The other pots are not affected while standing in the same room. I gave plenty of water to all plants before I left but took care that there was no water in the coaster.

Search results suggest it might be calcium carbonate or niter. But I guess it's mold because it's hairy. So my questions are:

  • Can someone distinguish if it's mold?
  • Should I just remove it or change the pot?
  • What could be the reason – should I dump my bag of soil and get a new one?

Flower pot with white growth

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These are naturally occurring salts from the water added to the pot. As clay is permeable it absorbs the water with the salts. As it dries and the water moves into the soil the salts are left behind and make the crust or layer that you see.

To remove this wipe the rim with a cloth that has been soaked in a dilute mixture of vinegar and water. About 1 part vinegar to 3 parts water should do. Repeat if necessary.

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  • Thanks for the quick response @kevinsky! Only thing I'm still wondering about: Why it appears now at several pots at the same time. I mean the difference was that the heating was low during I was out. So the room climate was colder and more humid for two weeks. That's another reason I was afraid it might be mold.
    – johjoh
    Commented Jan 6, 2021 at 9:16
  • @johjoh might be due to the reduction in room humidity which is typical for this time of year
    – kevinskio ♦
    Commented Jan 6, 2021 at 12:48

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