I just use a peat/coarse sand mix, and then take about a tablespoon worth
of sphagnum from another pot, cut it finely, and spread it around the top
of the new pot. It takes off and usually covers the top within a month
or so. I collected a handful of sphagnum from a local bog 6 years ago
and haven't had to do it again since. (And since I did this in the
winter, I inadvertently got a colony of hibernating stinging ants, which
rushed out onto my hands after I opened the bag at home, having had an
hour or so to wake up....:( )
Bob Beer