Angela,
They're difficult because they they seem prone to crown rot if watered from the top and are extremely sensitive to commercially available fertilizer salts in irrigation water. We grow the seedlings in 4" x 4 " net bottom pots sitting in 1" of RO water, and fertilize every week with rain water containing small amounts of dissolved bird droppings (collected from our roof) The rain water is stored in one gallon plastic milk bottles. Using the commonly available fertilizers seems to be the kiss of death for this species, especially in the concentrations commonly applied to our other Phrags. Since the mix we use contains a good amount of milled Canadian sphagnum moss, a thick layer of moss soon covers the mix surface. The plants get a small amount of nitrogen from the amine compounds secreted by the roots of the moss. The mix we use is a combination of quartz sand, non-coniferous charcoal, milled sphagnun moss and small perlite. Each spring, we top-dress each pot with ash produced by burning dried weeds from the prairie. Fellow ST member brasphrag has also had success in using a similar mix and probably has more experience than anyone in growing this species well. When we have seedlings to sell, we always include fairly detailed growing instructions with the plants.
