"K Barrett" wrote in message news:kMSWc.39230$9d6.6767@attbi_s54...
Name one orchid that doesn't want at least a 10 degree change in day/night
temps in order to flower.

Want or need? Off the top of my head...

Phalaenopsis bellina and P. violacea
Chiloschista lunifera
Psychopsis papilio
Oncidium Gower Ramsey
Cattleya walkeriana
Paphiopedilum (various mottled leaf species)
Polystachya pubescens
Polystachya vulcanica
Brassia verrucosa
Dendrobium antennatum
Cirrhopetalum curtisii
Sophronitis cernua
Neostylis Lou Sneary
Stenoglottis fimbriata

All bloomed reliably for me under lights without a significant
temperature drop at night. I'd suggest that the majority of lowland
tropical orchids do not require a temperature drop to initiate
blooming. Blooming could be triggered by a variety of stimuli:
increased light simulating defoliation of deciduous trees in the dry
season, reduction in watering, subtle changes in day length, or simply
maturation of the newest growth.

Plants from monsoonal climates are probably more likely to bloom in
response to cooling. Some orchids do bloom reliably after a sudden
drop in temperature (Dendrobium crumenatum, for example), and
certainly a temperature drop in the autumn may help others
(cymbidiums, hybrid phals) to spike, but there are lots that don't
require it. Since cooler temperatures in the autumn usually come
bundled with shorter days and reduced fertilizing, I think its unclear
exactly what the plants are responding too.

Orchids that are CAM plants may require a temperature drop for
efficient photosynthesis, and highland tropical plants will want
cooler temperatures at night. But those are daily, not seasonal,
requirements and are not directly linked to initiation of blooming.

Nick
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