Deciduous orchids, what triggers?

[Ross]

I have two Dendrobium anosmum (superbum) which are deciduous. Every year about this time (mid to late October) I begin withholding all water and fertilizer to cause dormancy and leaf shedding. This year I noticed that they are beginning to turn yellow and shed leaves on their own prior to going dry. This made me wonder just what exactly are the triggers? I presumed lack of water corresponding to dry season in SE Asia. Apparently not entirely. It can't be changing day length since they are under CF lights to extend natural day length. They are getting full sun supplemented by CF lights. They are growing indoors and temps have been cooler of late. Maybe temperatures? Any thoughts?

[Tindomul]

Ambient humidity?

[isurus79]

Ive read articles that claim that cooler temps are more important to dormancy in Dend ansomum than water levels. I guess the author that Im thinking of doesnt really cut his watering down that much over the winter, but gives his plants cooler temps and they flower just fine. The plants also keep more of their leaves using this method as well. Im too much of chicken to try that method out though (I dont want to risk a years worth of flowers), so I cant vouch for its effectiveness!! It kinda sounds like your experience backs up this theory though. Interesting question.

[Phantasm]

I have many dendrobium species, and the decidious plants always start to drop leaves about this time every year. In my situation, it seems to be a combination of temperature drop and diminishing daylight. I have not yet cut back my watering, but I usually do this anyway when the weather gets colder, so it's a natural progression. Under lights, it might be a bit more difficult since your conditions are pretty even compared to greenhouse conditions.

[Gin]

Mine are yellowing too , they have recieved lower Temps. but still the same watering (less when cool) Gin

[Ross]

So are we concluding temps have more to do with it (maybe day length) than water? I find this fascinating.