Hi Federico,
You can get seed from one VFT but you need one that has several
(many is even better) flowers/buds on the flower stalk. The pollen
is good on the first day (maybe the second), and the stigma becomes
reseptive the second or third day. To get seeds use a small brush
to gently move the pollen from a new flower, they open in the morn-
ing, to the older ones. I'm not sure how long the stigma stays resep
tive, but I always get seed be moving pollen onto a flower during
the second and third days it's open. Because the flowers tend to
open one or two at a time it is easy to get many seeds.
Dave Evans