Nights into the 50s F (roughly above 10 C but below 15 C) with days in the 70s F (roughly below 26 C but above 15 C) for a couple of weeks Are generally what I've read that induce good spiking and I can attest to that since after the cool weather we've had here I now have 5 phalaenopsises coming into spike, one plant is only about 2 years old (it's a keiki, so it matured much quicker but i'm still in shock, i did not expect it this year, it's incredibly small compared to the mother plant) and one plant is even sending out spikes.
A shortening of day length can also induce spiking but it won't be a very fruitful spike, last year I kept one of my phals inside all year with consistent temps and although it was a large, quickly growing plant, it only produced 2 flowers. That spike persisted through until this year and is now branching, so I'm going to see if it produces more flowers this year with the temp changes.
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