Well, I dropped one of my orchids and broke the clay pot it was in this morning. No damage to the orchid, thankfully!
However, on picking up the pieces, I discovered that the pot was actually made of some sort of grey clay, and looks like it has been dipped in terracotta color to make it look like a real terracotta pot. Now, these are cheap pots I got at Lowe's. The 3in. ones are $1.47 and the larger ones - 5in. or so - are $2.59 if memory serves. The clay does absorb water, so I'm assuming they "breathe" like the real terracotta ones do.
I'm not overly concerned, except that they might be using some sort of oil-based stain for the coloring, which might not be great for the orchids long-term. That being said, they also have clay pots at Lowe's that are the grey color, so maybe they are not stained. I'm thinking I'll go get one and satisfy my curiosity.
Here's one of the pot shards, and below that a piece of a real terracotta pot. Opinions or ideas, anyone?
Clay comes in all colors. Terracotta is nothing more than baked clay (the literal translation is baked earth). Your pots may be coming from an area where grey clay is more common, ergo cheaper, and an over-wash layer of red clay was used.
Sometimes when pots are being fired in the kiln changes in temperature or variations in the level of oxygen can discolor the clay. I seem to remember the technical term for this is "carbon coring." It does not indicate the presence of lead but may mean the pot would not be as sturdy as one that was properly fired.
About a year ago, I noticed that the clay pots I buy (mostly from Home Depot) get a black, somewhat slippery coating after a couple of weeks, which then progresses over months to what looks like algae of some sort. This is not in a greenhouse, but in the home. Never happened farther back in the past. I also notice that these pots aren't made in Italy or Portugal, as they used to be, but China. I haven't cracked one yet, so don't know what the innards look like, but I think these pots are coming with some sort of spores or something on the surfaces or imbedded in the suface. Not too happy about it.
Mark, you should be able to disinfect them with just a short soak in a mild bleach solution. Or scrub 'em with a bathroom cleaner containing bleach. Be sure to rinse them well, or soak them again in plain water to take out any residue from the cleaners. Orchids don't like soap or salts.
I haven't noticed any problems with my clay pots, but of course sun also inhibits fungal growth and mine are all outdoors.
Thanks, Elaine, for the tips. I have thought of the bleach thing, but then forget only to remember when the plant is in the pot!! I do worry about bleach residue (I don't need any help killing orchids), but I guess if I rinse well and let dry over several days, the chlorine should dissipate . . .
Orchids are surprisingly tolerant of bleach/chlorine. I had a couple of orchids spend the entire night at the bottom of my freshly shocked swimming pool two years ago and they are both living and blooming today.
Its usually the salt in the tap water which builds up which they dont like, im not sure if pools have alot of salt in them. I usually use tank (rain)water to water my orchids but my tap has been out of action so ive been using tap water for months and i can defenatly notice the white building up on the bottom of the pots, i find im repotting more and flushing more with tap water. i'd never had a problem with it using tank (rain) water. Is this weird, maybe im imagining it. hehe!