Phal schilleriana is an 'extreme' case, but it illustrates so well what old flower spikes can produce. My dad had one, which eventually bloomed:
- From main plant
- From 2 or 3 keikis on old spikes from main plant.
- From 1 keiki on old spike from the largest keiki.
Most hybrids are not as prolific. From close to 55 years of observations, it is my impression that:
- Whites rarely produce anything on old spikes.
- Yellows often extend the spike.
- Pinks commonly produce a side branch.
However, if nothing happens in 3-4 months, it is unlikely to occur.