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!
Diane

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!

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.

Hi,

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.

John

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.
Thanks!
Enjoy your day!
Tonia

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.

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!

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

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.

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!

Angelas, are your pots used or new? If new, that's odd..Clay pots should be soaked about an hour before use. Toni

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?
Thanks
Nic

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.

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.

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.

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.

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.

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.

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.

Here is the mold on my lemon tree's pot. What should I do? :(

I would spray it with some hydrogen peroxide (3% concentration, usually found in pharmacies) or some rubbing alcohol. You could also soak a paper towel in rubbing alcohol and wipe the mold off.

Both hydrogen peroxide and alcohol (rubbing [isopropyl] or denatured) are great mold killers. Bleach also kills mold. A spritz of any of these products is all you need - no rubbing necessary unless you are concerned about appearance. Any fungicide you might have on hand is also a good mold killer

Al

I'm going to chime in here being that I worked with ServPro for 2 years and have dealt with lots of moldy items.

I actually am growing basil and celery in my house and have this exact issue. My problems are minerals mixed with mold growth most likely Stachybotrys. Typicaly the only way this can hurt you is having a compromised immune system.

Now, bleach, alcohol, and hydrogen peroxide in no way "kills" mold. Bleach only changes its color to clear or white. Alcohol makes it dry, and in turn flower and spore when it's disturbed (touching, brushing, dry wiping, etc.). Hydrogen peroxide does nothing. I've heard people say sunlight "kills" mold, again untrue.

Thee one and only method of "killing" mold is use of a fungicide and removal of spores and hyphae (the rooting system of fungus). Spore and hyphae removal requires agitation (i.e. brushing and clean water or vacuuming, the second is not recommended unless you have a vacuum dedicated for just mold cleanup as cross contamination could result from general use continuing after cleaning up mold).

To solve my issue once a week I wet, scrub and rinse the outsides of my pots. It has helped reduce growth and spotting.

Unfortunately spores are all around us, in the air, in our homes, and definitely in the potting soil and already on the clay pots at time of purchase. Good luck reducing the mold growth on your clay pots. I hope this has enlightened someone about mold growth and cleanup.

I have no mold issue on terra cotta pots.

I use the 5:1:1 mix and get some slight discoloration here and there, but no mold.

If you have mold growing, you're either watering too often or have a soil that's too water retentive.

Hey all, I have a question. I have this type of white residue on all my clay pots, including ones that have mint, oregano, curry, and aloe. If it is mold, could there be potential problems with ingesting the herbs or using the aloe for skin care?

I'm 56 years old and have NEVER experienced this situation with a clay pot until recently. I bought the pot at Homegoods, discounted. To be honest, it looked diseased (discoloration, thinking it was ok?), you know, Homegoods would never sell a product that had a living disease, and I thought perhaps it was supposed to be part of the naturalistic, terra cotta charm? As far as I'm concerned, this has to do with the clay used. Perhaps it wasn't cured long enough? Who knows what they are actually using to produce these pots? I have never had a clay base absorb so much water before! All of you gardeners and scientists I think you are on the wrong tract. With everything I've read, you thinking it has to do with soil, I'm telling you, it has to do with the vessel.

I soak mine in a 5 gallon bucket with about 1-2 cups bleach overnight.

Any terra cotta pot used, if used long enough, will develop a patina on the outside. To some degree, the temp to which the pot was fired, the clay used, and wall thickness has an impact on how quickly this occurs, but it WILL occur if the temperature it was fired at wasn't so high as to render the pot walls gas impermeable.

You need to use at least a 10% solution of household bleach for it to be effective as a disinfectant/sterilant. When you soak your pots in a bleach solution, do it in the shade, as sunlight quickly destroys bleach's antiseptic properties. After soaking, a quick rinse and a day in the sun will eliminate any residual effects the bleach might have had.

Al

Well I have two 10 inch square, black glazed pots. I got them on sale and forgot to wash them I planted snake tongue plants in them. I have since been battling this white stuff growing on them. It is not salts like a lot of growers say. It returns and spreads if you are not vigilant. I have used washing the outside with full strength vinegar and spraying it with herbicide. Nope. Still comes back in new places no matter how I do it. So then I used some glaze to paint over it, more like acrylic clear paint. Nope. Bled right through that. And the I used Rose Shield. So far so good. Seems to work. But still early. It is not salts though because these are new plants and brand new soil. If it comes back I guess I will have to change the pots and soil, and hopefully I won't have to do that. Plants seem happy.

The pots themselves have high levels of salts in them. They need to be soaked for a considerable amount of time before use (maybe even with lemon juice or vinegar added), otherwise this will be a continuous battle. Plants that I leave outside to get rained on all season cease to have this problem even if I forget to soak them before planting.

Vicki

You said that pots are glazed?

It could be one of the chemicals used when glazing. Did you try washing it off with bleach? Do you have some photos showing the white stains?