In my area (Central Florida) most species are grown in a mix of equal parts
fine grain fir bark/charcoal/tree fern fiber. This applies to highland
species (which are generally grown in baskets) and lowland (plastic pots)
alike. I personally do not grow any Nepenthes in sphagnum because in my
climate it rots very quickly and the roots will soon be in an anaerobic muck
which may kill the plant. This mix usually is good for about 2 years and then
must be changed. As this is a very well drained and porous mix, it must be
pre-soaked at least 24 hours before use. It will also mean regular watering
in warm weather. Species that respond well to this are quite varied in
habitat in the field: N. alata, ampullaria, bicacarata, tentaculata,
mirabilis, veitchii, macfarlanei, maxima, lowii, truncata and many others.
The main difficulty comes in trying to grow the species restricted to
ultra-basic soils. This includes N. rajah, burbidgea, macro-vulgaris, and
also stenophylla (N. fallax?) and villosa (although they are not confined to
these soils). So far in cultivation here, ultra basic species have responded
to two types of media. One is 90% 3mm silica-gel mixed with 10% of the
standard mix. This is NOT the silica gel that dissolves in water, or the type
with indicator crystals in it. It is white to clear and very hard. It must be
hydrated in a high humidity envoronment for several days before use, for if
immersed directly in water it will fracture to dust. The other medium is 90%
high-fired clay used in aquarium filtration and 10% standard mix. One brand
of this is called Biopur. It must be crushed as it comes in little cylindars
and roots might get restricted in the holes. BOTH of these media are
EXPENSIVE, but the silica gel can be bought in bulk, the other (so far)
cannot. This is not a problem if you have only a few of the ultra basic
forms, most of which are still fairly uncommon. Since N. rajah is now in
tissue culture a series of media should be experimented with to determine the
optimum soils.
Lastly there is the little understood problem of N. northiana which has not
really responded to any soil with any great vigor. Neither the above
mentioned soils nor the addition of limestone (marble) has produced growth
consistant of plants in the field. N. sumatrana is another plant that
survives but is not terribly happy about cultivation.
Other medias worth experimenting with include rock wools and aerolite. Media
to avoid: redwood fiber, cork, peat (to dense and acid), lava rock, turface.
Coupled with media should be high quality water (R.O. or similar) which is
absolutely necessary for the ultra basic species.
Again this is what works for me in my area of the world, and I am still very
much learning about Nepenthes.
Cliff