Once you get the hang of using sphagnum as a sole medium for Phals, you'll be amazed at how great the stuff is. By comparison, when using sphag. to bark mix, if it's used correctly and in the right conditions, side by side, I've found better results with sphag....more growth 10 fold than with bark BUT there's very little room to screw up with it. It will be very unforgiving if you do, unlike bark mix. That's the tricky part! Sphag.. mixed in the bark mix is an excellent compromise also.
I did a lot of experimenting this past summer and don't know what exactly I can credit the growth on this Phal. to but it's been growing in nothing but straight sphag. (mixed with sponge rock to prevent it from getting water logged). It now has 3 basal keikis, 3 aerial keikis and one keiki was recently removed and now growing separately. It's huge, more than doubled in size since March.
Phals love getting wet but they need a constant source of good air circulating in their pots to really thrive. That's where you have to be very careful when using straight sphag. which can easily get weighted down and suffocate those roots if not careful.
Here's mine. The second pic includes the keiki I recently separated from momma. I have the keiki growing in a combo of bark and sphag. I'm not always so brave.
