Hi Angela,
I've been following this thread for awhile now and thought I'd jump in to let you know how we are currently growing Phrags. at Fox Valley.
1)We no longer grow Phrags with pots sitting in trays of water. We found we had better growth by top watering every other day; summer and winter. This practice assures a good supply of O2 in the root zone.
2) We no longer use Orchiata. After a two year long test period, I was not happy with the results in terms of root growth and went back to a standard seedling grade fir bark mix - ratio 8-1-1 (bark-large perlite- #3 size charcoal). The plants are growing much better with that change. Not sure why it works for some who use it, but it didn't work well for us.
3) We fertilize every other day, alternating K-Lite, MSU for RO and Peter's 30-10-10. We add whichever fertilizer we are using to 50 gal of RO +5 gal of Chicago water (for it's micro-nutrients) and aim for a TDS of 200 ppm. We have a 55 gal plastic barrel which we pump out of when we are fertilizing. This gives us about 70 ppm N2. On days we are not fertilizing, we flush the pots with straight Chicago water, which has a TDS around 220 ppm.
4) Our gh summer night temps are whatever the night temps are outdoors; rarely as high as 80F, but normally around 65-70F. Summer day temps are dependent upon the outdoor humidity because we use an evaporative cooler, so normally 72-82F. In winter we have night temps of 60-62 F and day temps of 70F + whatever the sun provides with minimal shading; sometimes as high as 78F.
5) We use 60% Aluminet shade cloth in summer, and light levels are around1,000-1,500 fc because the gh is shaded partially (20%) by surrounding shade trees. We remove the shade cloth on the 15th October and apply shade paint to give us a light level initially of 1,800-2,200 fc. Obviously, this light level decreases significantly as the sun's angle of incidence decreases. All readings taken at noon on a sunny day.
6) We use only plastic pots. Clay pots are fine for most orchids, but I think if your gh temp at night is in the low 60's and you have vigorous air movement, because of evaporation clay pots get a lot cooler than the low 60's and no slipper orchid likes cold roots.
7) Make sure you temper your irrigation water in winter. I lost a good amount of seedlings a couple of years ago using cold (48F) water out of the barrel. I now use an aquarium heater in the barrel in winter and heat the water to 68-70F before irrigation.
Sorry this is so long, but there are some things that absolutely have to be controlled if you're to optimize Phrag. growth..... It's not the only way to grow Phrags., but it's the way we grow them. Hope this will help.......