Mold on clay pots

beachlakegrower(5b PA)March 4, 2006


I am pretty new to houseplants and new to this forum. I have a few plants in my apartment in clay and plasic pots. Aesthetically, I prefer the clay pots but I have noticed that 5 of the 6 clay pots that I have seem to have a whitish/grayish powdery sort of mold growing on them. I'm not allergic to molds, but I still want to avoid this from happening.

I thought about wiping the pots down with a bleach solution, but I am not sure if this could harm the plants or if it would offer a long-term solution. Not to mention that bleach is nasty stuff to deal with anyway.

Has anyone had a problem with mold growing on their clay pots and is there something I can do to stop the mold that is growing now and prevent this from continuing in the future? I appreciate any feedback. Thank you.

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canttype(0b (Cold North))

I'm not certain that the white powdery stuff on your pots is mold. I'm under the impression that this is caused by salts and fertilizer residue.Clay pots seem to absorb these things. The same whte stuff can lie on top of the soil..... Which is my cue to leach my plants or replace the soil as most plants can't take too much salt. Unglazed clay pots can be deadly to African Violets because they really can't take the salt.

I use bleach to clean all my pots before planting in them. It's a good soak/scrub for previously used clay pots to ensure that disease/molds/fungi don't stay and damage a new plant. That does'nt seem to effect the plant being planted into it, but to use bleach while the plant is residing in a pot? Maybe not a good idea?

Have they been in those pots for awhile? Is it time to repot your plants in clay? Change the soil and wash the pots?

Hope that helps you somewhat!

    Bookmark   March 4, 2006 at 12:50PM
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rhizo_1 (North AL) zone 7

Ha! And Martha Stewart conducts CLASSES in how to make clay pots look aged!

Anyway, I suspect that Diane is right about the soluble salt build up on the outside. These are leachates from your water and/or fertilizer. In some conditions, an algae will grow on that, too.

Rather than bleach (which would not be good for you or your plants!) you might want to try vinegar. I would protect the plants and soil while you are doing this, by the way. But spray some vinegar on the pot and take a scrub brush to it, rinse off with clear water. When you do a repotting, you could soak the pots in vinegar for awhile, scrub, rinse and allow to bask in the sun for a couple of days.

Perhaps some of the others have some good ideas, too!

    Bookmark   March 4, 2006 at 1:17PM
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greenelbows1(z9--so LA)

I like to use those green scrubber things that are sold to clean your (cooking!) pots with. Comes right off if the pot is moist--doesn't work so well if it's dry. I didn't remember Martha Stewart conducting classes in aging pots, but I know I've read lots of hints like brush them with buttermilk. Once someone brought a beautiful multiple planting in a pot she'd aged carefully to a flower show, and we had to disqualify it because the schedule said 'clean' pots. We told her she could clean it up and it's be fine, but she said it had been too much trouble to get it that way. Think we probably discouraged a potential exhibitor. Always felt bad about that.

    Bookmark   March 5, 2006 at 12:52AM
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beachlakegrower(5b PA)


Thanks everyone for offering your advice. I still think that some of what I am seeing is mold but irregardless, I will try the vinegar and a green scrubby to see what kind of results I get. Thanks again.


    Bookmark   March 5, 2006 at 7:52PM
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artzypantz(z5 / IOWA)

Hi Beachlakegrower.........i was wondering how you came out on your mold looking stuff? Maybe not enough time has passed, but when theres been ample time would you please let me know?

I have the very same problem with only 3 out of the 8 clay pots that i use. This has been going on this way for a year now. Most of my clay pots have some hard crusty white (lime?) build up on them, BUT these three are different. They do not get the same food, have the same soil, and get the same water, but all 3 have this very fine white fuzzy feeling powdery feeling stuff at the top rim and the very bottom of the pot. It wipes right off with your fingers, and does NOT go onto the soil. 1 plant is cyclamen, 1 is bamboo, the other is some sort of vining plant. The cyclamen gets the acidic type food & i do give it a bit of blooming food now & again, the other two get weak regular miracle grow. Plants seem to be doing okay.
We have no water softener, but our water is very limey. (I buy a new coffee pot every 3 months due to lime build up in the metal tube that sits under the heating element, i just can't wait over an hour for a pot of coffee to brew!)
Every one told me it wasn't mold also. (Looks like mold, sorta feels like mold.)
It has been a total mystery to me!
Any how if yours sounds like mine i am interested in what you've done & how it turned out for you. Please post when theres been ample time to know.
Enjoy your day!

    Bookmark   March 14, 2006 at 1:23AM
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I am having the same problem with mold on my pots. I have used these type of pots for years and have never had this happen before, and it is truly mold. I had a velvet plant in one of them and it wasn't doing too well, when I took it out to replant it mold was all over the roots, once it was repotted in a different pot it is doing much better. I will try to scrub the pots clean this weekend with a vinegar solution and see what happens. I was wondering if it may have something to do with the soil that I'm using, although I do not use any specific type. Anyway peculiar thing.

    Bookmark   December 24, 2006 at 11:22PM
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beachlakegrower(5b PA)

I tried the vinegar, but the mold came back again. I considered bleach but thought that might harm the plants if some residue was absorbed into the clay pots, and I'm not much for using bleach anyway if I don't have to. I think some of what I was seeing may have been soluble salts building up, as someone else suggested, but I am sure at least some of it was mold. I didn't have that many plants at the time, so it was not a problem to swith to plastic pots, which I have stayed with and have gotten use to. Good luck!

    Bookmark   December 25, 2006 at 3:33PM
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dufflebag2002(Calif. 91607)

Try more air circulation and the other suggestions above. Molds come from too much consistant moisture, and spores I think the bleach would be a great help. Let the pots sit for 20 minutes in the bleach water, rinse and dry. Put the pots and soil in the micro wave for 5 min. on high. I have never had this problem in my own greenhouse. Norma

    Bookmark   December 25, 2006 at 8:09PM
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Beach, you have to appreciate that clay pots absorb water unto themselves....thus water you give your plants, some is absorbed into the clay itself. Over time, the moisture within, and without, can dry to the crusty white you see as the results of salts from the fertilizer.

This is a very good example of why you should not allow drainage water to sit in the saucer below. The water that drains, some of it contains those salts, and should be dumped.
When you allow the water to sit---and be re-drawn up, you are then giving the plant again, the salts it just got rid of.
Because the salts are in the water, some of it is absorbed into the clay...and sooner or later, shows itself on the outside of and the inside walls of the pot.

Bleach is a very good cleanser for the pot....but not so good for the soil within it. If you wish to remove the plant, clean the pot, then give it fresh soil, that would be the better way....but if you consider doing this, wait until spring because any re-soiling you do now will encourage growth....and with the low intensity of sunlight, any new growth would have a tough time making it.

Better to do it in and around February/March when the plant can be allowed to grow new leaves from the increased intensity of sun that is now high enough to promote growth.

    Bookmark   December 25, 2006 at 9:13PM
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I am really getting into houseplants for the first time, and I read about the benefits of clay pots, so I went out and bought three for my three new plants when they were ready to be repotted. One of the pots had a bit of white crust, but it was more discoloration than anything else...or so I thought. After potting my plant and watering it, within a couple days the "discoloration" was standing out a bit, with a fuzzy texture. I wiped it off. My husband and I went out of town for a couple days and when we returned I found the fuzzy white spot had returned and the entire pot was covered in a fine layer of what was definitely mold. I took a dampened a cloth with water and vinegar and wiped the pot clean. My other pots are showing no signs of any mold.

My husband suggested I'd brought that pot home moldy without realizing it. When I thought about it, I did buy that pot at one store where they kept the clay pots outside, and the other two pots were bought at a different store where the pots were kept inside.

I may buy a new pot. Good thing the things are cheap!

    Bookmark   April 29, 2007 at 10:02AM
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Angelas, are your pots used or new? If new, that's odd..Clay pots should be soaked about an hour before use. Toni

    Bookmark   April 29, 2007 at 7:18PM
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An old thread but lets see if I can inject some life back into it.

I have recently repotted 2 plants into clay pots, the pots had previously had some mini conifers in them and were outside, they have been empty for a year, still outside. I had 2 indoor plants that were out growing their glazed pots so had thought the ceramic ones would be ideal. I repotted them about 3 weeks ago and they've been growing mould ever since. I wiped the outside of the pots down about 10 days ago with mouldkiller and a small amount of bleach and was hoping that would work but it has come back unfortunately. I've done the same again but it bit more vigourously and thought I'd do some searching on the interweb for ideas, I will try vinegar if/when I see it again, any other hints n tips?

    Bookmark   October 2, 2011 at 12:23PM
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I have both salt deposits and mold on my clay pots. I know what mold looks like both macroscopically and microscopically and what I have is indeed a mold issue. Salt should not be fuzzy or have gray spots. I didn't want to use a mold killer as I was afraid it would leach into the soil and contaminate my plants. So, I tried wiping the pots down with tea tree oil; it staved off the growth for awhile but now it's back with a vengeance. I was told by someone who is majoring in plant science to put the pots in a sink and slowly drain the soil with water for about ten minutes as it should help with the salt deposits. However, due to the mold, I assume I will need to change the pots which is not going to be fun as I have delicate seedlings. Yes, any hard, white scaling seen on clay pots is definitely salt, but you can still have mold growth. Despite hearing that soaking the pots prior to use can help this issue, it kind of goes against what I know about mold and in fact, may stimulate the spores. I think I'm going to go back to using plastic pots.

    Bookmark   April 11, 2012 at 2:05AM
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I have a lot of plants in clay pots in my house and office. I have had the white film appear on the pots also. I thought it was mold but it may be salt, not sure. I read that if you spray hydrogen peroxide on your pots and also the soil of the plant that it will kill mold and you won't have a problem with it. I've been spraying it for a few months and my plants are thriving. It makes the white film go away. It will come back in a month, and I just spray it again. It's great.

    Bookmark   May 26, 2013 at 8:34PM
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wow this is an old post!!
If you want pristine clean clay pots plant in plastic and put the pot in the clay pot: pot in a pot.

    Bookmark   May 27, 2013 at 8:27PM
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I have a "tree" can't think of its name, but I got it at my local grocery store. Anyways I transplanted it into a 10" clay pot that was glazed, and I have an unglazed clay saucer. Water never sits long in it as I keep my plant thirsty, but a while ago after having the saucer on a raw wood table I moved the plant and mold of all different color was growing under where my plant was, so I bleached the table and the underside of my saucer since thats where the mold was. Now I only water my plants with purified water from the store, but Im now noticing that I have dusty white patches on the saucer and Im wondering what it is, I am allergic to mold so I don't know what to do to keep this from happening.

    Bookmark   September 14, 2013 at 1:56AM
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This is interesting. Are the plants suffering? Are they affected by the white powder?

I came here wondering about the white powdery dust growing on the unglazed terra cotta pot for my African Violet. I chose the terra cotta pot because, one, that's what this guy who grows AV's recommends on his blog, and two, expensive pots made special for African Violets are porous like terra cotta. You're supposed to water African violets from the bottom up if you can, so I fill the saucer with water and let it sit.

I've used a lot of fertilizer this time, and I'm pretty sure that's why it's flourishing instead of dead, like usual. So the salts/minerals leech idea makes a lot of sense to me, since there's so much stuff in the fertilizer.

Of course that doesn't account for the grey spots someone mentioned upthread. Except that expensive gourmet salts sometimes are a grey white. It's the other minerals aside from the sodium.

As well, if you've ever done a grade school salt water crystal experiment you can see how the salt crystals grow kind of lumpy. I can imagine that seeping through the tiny pours of the terra cotta the salt might build up and look maybe fluffy?

I dunno, unless the plants are actually suffering maybe the pots should be left alone. I'm just so happy about this first ever success with this AV that I'm not willing to do something like scrub the pot. Much less re pot it. Heck no.

    Bookmark   November 3, 2013 at 5:21PM
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journeymom, like what they said above, the pots it could be starting with leachates from the soil. As the water evaporates through the pot, the minerals dissolved in it remain. Depending on what the minerals are and how good the air circulation is, stuff might grow on the surface, using the mineral deposits for food. Most commonly, green algae grow, but if it is kept damp enough, long enough, then other things might form.

I have an underground stone wall in the house with a certain kind of stone in some places that must have microscopic cracks in it. The water from the ground comes through it and dries. (The stone is never wet.) The minerals left behind can grow to an inch before they fall. The tiny crystals have a positive end and a negative end, and they grow by making a weak lattice. This "beard" on the rocks looks every bit like mold, but when you take it between your forefinger and thumb, it turns to cement powder; dry and quite dusty. For this to happen it takes 6 months and no wind of any kind.

    Bookmark   November 3, 2013 at 5:41PM
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I usually get mold on my clay pots (jade and schlumbergia), but last winter I dealt with a bought of powdery mildew and sprayed a fungicide on it out of curiosity and the mold disappeared. It was definitely mold. Since then I've repotted the schlumbergia and been keeping the jade very dry=very little new mold growth.

I've decided clay is only for very dry succulents, like my jade and lithops.

    Bookmark   November 3, 2013 at 9:27PM
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I clean my clay pots with Lysol cleaner. It isn't so intense to me as bleach, which is what I used to use. It's also easier on hand tools if you need to disinfect them. If the pots are really encrusted I use the vinegar treatment mentioned above. Sometimes it takes a couple of treatments to get a clean pot. I use clay for a lot of plants, but then I have a drier clime than people in the east, and I haven't had too many mold issues.

Just a last thought, molds really like it too be cooler. For clay pots, I wonder if maybe a period in a warm oven would fix them up. I don't know if they were really wet if it would get them to spall or not, so just try one at first. Oh, better take the plant out and wash the pot first also. Hot potting soil really stinks.

    Bookmark   November 4, 2013 at 9:04AM
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