Well I have the same issue here on relative new Phal.
When I reppoted them I was unable to stuck those parts of the roots in the bark as they were before. Futhermore, when I got the Phal. the potting mix had some Sphaignum moss in it.
I don’t know much about Orchids, but I believed it could have been damaged due to the change in the growing environment as roots don’t realy adapt to environment changes, the plant trows adapted roots instead, and the old ones usually dye. Any ways that it is what I got from doing some semi-hydro culture. I was wondering if small environment changes were enough to make that process happen ?
Or I believed it might have been spider mites but all the leaves are very nice.
I actually repotted on of the 3 Phal. that had that in a larger pot to cover the roots and left the others like that. (experimenting here
)
I also wonder if maybe I was not watering my Phal. enough, I too water about every 5 to 10 days mostly every 7 days and I allow the bark to get realy dry.
P.S. Watertiger hope your are ok with me adding questions to yours about this issue.
Hybrid Mode
