Dendrobium aggregatum max. night temperature for blooming
 

I have several divisions of a thriving D. aggregatum that I'm trying to bloom. They're under lights and have good leaf color (PPFD around 250 for 14 hours). My difficulty is the winter night temperature is controlled to a minimum of 60 F, for my diverse collection. Has anyone been able to get them to flower at that minimum, assuming they will be relatively dry and bright?

I can't answer your primary question, but that long a day length in winter might inhibit flowering of a number of orchids. Many light growers give 10-11 hour days in winter.

I agree with Estacion.

14 hours of light will prevent flowering in spring.

The important thing with temperature with orchids is never the exact temperature, they are very tolerant of a wide range. The important thing is a differential between day and night. During the day you want it warm to encourage photosynthesis and at night you want a drastic cool down to preserve energy while the orchid opens its stomatas and does air exchanges. The amount of cool down needed varies from orchid to orchid. This cool down at night increases ambient humidity which is highly beneficial for the orchids. On really hot muggy days the orchids transpire and lose more moisture at night than they can gather during the day and become dehydrated.

If you grow your orchids warmer I personally find it beneficial to water them in the evening. This goes againt what most would do. If it is kept cool you water less and in the morning so the orchid is dry by the time it gets cold. But in warmer conditions you want to spray the orchid lightly in the evening to create a bit of evaporative cooling during the night. But I don't think it matters too much.

Anyway why do I say the temperature is not that important? Just because I have seen it being grown in Florida and Jamaica outdoors. All you have to do is see how cold it gets in these locations in winter time. It never gets very cold in these places.

Look up a youtuber called Orchid Doc: Growing Orchid in Jamaica, check out her video from 7 months ago which has had 20k views on Mar 20, 2023. 5 minutes in she will give you her tips.

My grow room runs 76 to 78 degrees days and I pull it down to 60 at night. The photoperiod may indeed be too high for blooming; I've read that most orchids are not sensitive to light duration, but it bears checking. I'm putting one of my D. aggregatum and one D. loddigesii out in my garage where they'll be down in the 40's at night, and under a light that I'll set at 11 hours.