I've been noticing this odd, yellow-ish/rusty-ish substance appearing on the surface of the soil in many of my potted plants. The vast majority of my plants are cacti and succulents, but I've been noticing it with some of my herbaceous houseplants as well (i.e. Philodendron, croton, etc.) Tonight, I bought 3 more cacti and a succulent from my local Wal-Mart, and I noticed that ALL the cacti and succulents they had there have this stuff on the surface of the soil.
It looks like this: http://www.flickr.com/photos/ohsweetie/4420315361/
(Not my photo, but that's what it looks like.)
Does anyone know what it is and (if it's a threat to my plants) how to get rid of it?
I can't vouch for the soil the plants are originally potted in, but when I do transfers/repotting, I use an organic cacti & succulent medium. A number of my containers are non-draining, but I manage those plants' waterings very carefully; the weird fungus-looking stuff is in the draining containers as well.
I try not to water too often, but even as indoor plants the soil seems to dry out really quickly (I do live in a desert), so sometimes I find myself watering ever 2-3 days. (That seems excessive to me, but I go by the moisture of the soil.) I also keep my succulents and cacti in an east-facing window (some on the sill, some on a table just below the window), so they get an abundance of sunlight, but for only a few hours each day.
Because it's scorchingly hot out, I can't open the window to allow for ventilation and air circulation; instead, I keep the ceiling fan on.
I've been watering all my plants for the last year and a half with tap water (which I JUST read is no bueno for my plants); our water is pretty alkaline (although I don't know the pH) and saline (744 ppm).
It is fairly dusty in our home (at least by my standards, anyway), and I frequently have to dust off all my plants so they can breathe. I wonder if there's something floating around in the air/dust that contributes to the weird fungus-looking stuff on the soil surface.