This is an area of interest for commercial growers, so research has been done on the most commercial orchids. A quick search in Google Scholar gives a lot of reading material.
Murph and Bulbo, thanks for the info. I should have hit refresh before I responded to Ray, then I could have caught all of you in one post. This is all good info.
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Steve
I'm just hoping not to kill them!
Night length can be a trigger; temperature can be a trigger; water pattern can be a trigger; barometric pressure drop can be a trigger. It varies from species to species.
Most plants growing close to the Equator don't have a night length trigger, because there is so little variation.
Rain seasonality is a big trigger to a lot of plants from areas with dry winters and wet summers.
At least one orchid, Dendrobium crumenatum, is triggered to bloom by the drop in barometric pressure with thunderstorms.
__________________ May the bridges I've burned light my way.