Have you tried using a lime-scale remover?

Hi Purple, no I haven't but I've got some of the CLR in a spray bottle. Will try that, thanks!

Bleach is supposed to work..Depending on the material, some pots can go in the dish washer. Toni

Well the CLR worked great and removed almost all the crusty material very easily. I say "almost all" because there was a little very stubborn brown crusty stuff on some places, like the water line near the tray, that didn't come off. It seems that requires scraping it off with a blade.

I didn't use any bleach, but I have a couple glazed ceramic pots that are not glazed on the inside and that acquires a brown staining from the soil. Bleach might have worked on that.

Thanks again for the ideas.

I would not use bleach on UNGLAZED terra cotta, it's likely to absorb some of it (unglazed clay is porous, therefore absorbent).

Not sure the plants would appreciate it.

If it's just discoloration on the inside of the pot, other than scrubbing it well, I wouldn't bother more than that, not like the plant will know or any one will see it.

While acids (like vinegar or CLR) can be used to remove mineral deposits, and bleach can be used to remove organics, you should never mix the two. Doing so can release toxic chlorine gas.

^Just in case anyone was thinking about doubling up their cleaning power.