Well, first things first. True moss does not produce seed, but spoor.
Secondly, some spiecies of sphagnum are very rare and feild collection is very bad, but other spiecies grow like gang busters and field collection is okay, but not for the average person. These days, a lot of componies that sell live sphagnum and peat have this awsome feild replanting program that lets them get a whole new crop of live sphagnum every 5 years or so per location. Canada(sp?) is proticularly skilled in this methoid of resorce renewle and technically their moss is "wild", but they own the bogs. Mostly, be carefull where you get non-green varients from because all of those are thretond from over collection.
Also, the lovly thing about this moss, it is changes it's own enviornment. All you need is some water and some spoor and eventually a single cell thick webbing of baby sphagnum begins to grow. It's first goal? Changing the pH of the water
Then if focusses on bulking up. By then it's pH lowering factories (special cells) are fully working and it forcusses on building supplies of various bioweapons to combat illness and such. Once it is astablished it can make it's own spoors, the new spoors have an easyer time getting a hold on things and grow much faster. Cool yes? Anyhow, you won't need to worry about pH once the moss is growing well.
Finally, Sphagnum is just an awsome little plant and worth learning more about. Try running a search and you may find more info!