Here is my way to bring my vpt through the winter (a very cold and long one in
Germany):
The vpt is growing in an aquarium, since end of october indoor due to
outside temperatures less than 5\260C. I used an additional light, type
sylvania grolux with 75 W, distance to plant: approx. 20 cm (2/3 ft.),
and kept the soil nearly normal wet, as in summer. The normal
temperature was during the day (when I\264m at work) 15-16 \260C and
during the short period of 3 hours during the evening 20\260C. The
additional light was on for 12 hours in november and at least 9 hours in
January and vice versa up to march. The only special thing I did was,
that I supplied the plants with water only when the soil has been nearly
dry. The effect: the vpt flowered at least two times in march and is
looks very healthy now, what is valid for all my other plants too.
Unfortunately I\264m not able to say what kind of soil I\264m using,
because I bought it ready to use in a garden center ("OBI" - for german
readers).
Regards
Michael