Sue - i also acquired a grascillis keiki recently. My research found that they are not terrestrial, but rather grow on the sides of cliffs - where they receive higher than normal (for orchids, anyway) levels of direct light. so no terrestrial mix.
i've got mine in a 3/4 sphag, 1/4 osmunda mix, and its LOVING it. Good luck!!
Wogga, thanks so much for the info. I've spoken to 2 people in the past few days that have killed this plant! From what I gether, the are very susceptible to root-rot, so a terrestrial mix really doesn't sound logical to me.
I'll give your recipe a shot, thanks
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