oh my. wooly mams. i have had so much trouble with them.i can rarely ever get any to grow. they always just rot and die, or burn up in the sun (something you think the wooliness woud protect from.) i have one un-id`d one that is still alive that i rarely water and keep in 50% shade. it seems to be doing fine.

I don't think this is what you call call a wooly mam. M. parkinsonia. It is more of a short white needle-ish mam. It is easy in a gritty lean mix in half day summer sun and full day winter sun. It is almost in full sun now. just the height of the summer does it get shade from the overhang. I did kill a wooly rebutia this summer with too much sun. Ticked me off royally. I too thought that all that white hair would mean it was a sun lover. I was not aware of the difficulty with fuzzy mamms. Thank you for the warning.

in looking at habitat photos of a lot of these rebutias and other woolies in the mountains, I see them squatting in rocks that provide shade.

Thanks.
I had two, by the way, and one began to die as soon as I re-potted it in a sandy mix. The other one gets direct sun for a few hours around mid-day, and is thriving where it is.