Not growing this species in trays - just don't have the room; Most of the adults are growing in 3 1/4" square pots in an area that gets warmer and brighter than where we grow Phrag. besseae. We water this species twice a week; once with city water (Lake Michigan) for it's Ca/Mg content and once with our standard fertilizer water (in winter, this would be 90% R/O + 10% city water (LM) + 15-5-15 CaMg @ 50 mg/L N concentration). In warmer months, we replace the 15-5-15 with Peters 30-10-10, keeping the N conc. the same 50 mg/L. Not sure if this would work in conditions other than our greenhouse, but it's a starting point.