Here's a second photo.

Several years ago, I found some large ceramic serving bowls at Big Lots. They were very attractive, with a nice drip glaze on them, and came in sets of 3 or could be purchased individually. I bought several sets and a few from broken sets, then drilled holes in all of the bowls. Our bonsai club was having a fund raiser, so I purchased 4 lots of 20 dwarf conifers to sell at an art fair. I potted up the bowls with 1, 2, or 3 dwarf conifers, depending on their size, I did this in late April. I also kept a few of the conifer dish gardens for myself.

As the art fair became a memory, I noticed that none of the conifers were doing well - at all! In fact, all seemed to be dying. On examining the bowls I noticed there was some saort of material weeping through the walls of the bowls. I thought that very strange, for 2 reasons. The first was, I assumed that because the bowls were glazed ceramic, they would be impermeable to gas and liquids. I was obviously wrong on that count. The second thing that struck me as strange was the fact that something phytotoxic was used in making the bowls. It's possible that what was poison to plants might also be poison to people, and had I used these as serving bowls might never have noticed what was coming through the walls of the bowls.

End of the story is, I lost all of the plants I had in the bowls, even though I flushed the soil and repotted into terra cotta. These weren't cheap plants, either. Even at wholesale they were $20 each. My main concern was for the poor people who bought them at the art fair. I had no way of knowing who they were and have always felt really guilty about that whole deal.

It's possible that the material forming on the walls WASN'T phytotoxic, but did affect the pH of the soil significantly and in doing so killed the plants - I'll never know. Big Lots wouldn't give a refund, BTW.

All that to say I'm not really sure what's on your pot. I'm not sure if it's precipitants that were once dissolved in the soil solution and were deposited there after the soil solution made its way through an unexpectedly porous glaze, or if it's a chemical in the clay that attracts moisture from the air and forms chains of crystals like you're seeing.

How long have you had the plants in them? Are the plants doing ok, or do they seem to be suffering?

Al

Al,
Wow, that's pretty scary. Now I'm even more glad that I made the decision to place plastic pots inside glazed ceramic pots instead of placing my plants directly into the ceramic pots (it was more because all I can find is ceramic pots that have non-removable saucers... was creating drainage issues). I guess that's the "anything to make a buck mentality," even if it has the potential to be hazardous.

Planto

Hi....I know that you really have to watch out for pots and dishes, ceramic things that have lead in them.....I have heard of people buying coffee mugs and other dishes that contain lead...ceramic and glazed dishes and pot from other countrys can contain lead....I remember when I did ceramics if I did dishes or anything that was going to be used with food had to be glazed with a different kind of glaze that did not contain lead...could lead in the glaze on your pot cause this??? totally just a guess here....linda

Read through the link I'll leave below and see if anything about the way you're caring for your plants jumps out at you.

Al

Here is a link that might be useful: An overview

I also have similar issue, I wipe the pot every other days with dish soap and sometimes I add alcohol, it keeps coming back. in the picture that is how much white powder grows in 2 days. I just searched and found that it could be from salt build up and not harmful but i will keep doing research

Ningy - I know exactly what is occurring because it happened to me and our bonsai club. I'll explain. I purchased 4 cases (20/case) of dwarf conifers in the club's name to sell at a summer art fair. Prior to purchasing them I had discovered some serving bowl sets at Big Lots, a deep discount store that buys a lot of closeouts and end runs to sell. These were in sets of 3 with one bowl being about the size of a salad bowl, one the size of a vegetable serving bowl, and the smallest was about the size of a large soup bowl. They had a beautiful glazed finish accented with a drip glaze around the rim. I drilled drain holes in them and we had a club workshop (April) during which we potted them all up in the bowls using gritty mix. We were a few bowls short, so I used some of my clay pots. The plants quickly established in the new bowls and pots, no losses, and we sold all but 1 or 2 planted bowls and a couple of plants in clay pots, so the show went very well for the club. The club decided I would be the plants' caregiver until we decided what to do with them. Sometime in July, I started noticing the color of the plants was 'off', and I noticed some crazing (fine cracks) in the pot's finish. Soon, a white material started to appear on the outside of the pot. The material wasn't due to residuals left behind when the soil solution evaporated, it was due to dissolution of the material (from which the pot was constructed) into the soil solution. The material wasn't a salt as it was very high in pH. It killed all the remaining plants in the pots from Big Lots. When I bought the pots, made in China, I was so enamored of them I bought several for myself with the intent of planting them with small woody plants to give as gifts. I feel guilty about the poor people who bought the plantings from us, and even guiltier that they probably concluded they killed the plants when it wasn't even their fault.

The greatest horror is in the fact that these were sold as food serving bowls. Heaven only knows what sort of chemical concoction those bowls were made of.

My suggestion is to consider it an emergency and change pots, flushing the soil very thoroughly after the switch is made, then fertilize immediately with an acid-forming fertilizer. Foliage-Pro 9-3-6 would do the job nicely, from a single container, and should be appropriate for almost anything you're likely to grow.

Al