minimum winter daytime temperature for a cool growers

[drosera]

Hi Orchidboard people! I need some advice based on your experience. I know that some cool-growing orchids need low winter night temperatures around 10-12 C. But what is the minimum daytime temperature for them without causing health problems? I am thinking, for example, of some Dendrobium species (D. nobile, parishi, aphyllum, primulinum, etc.). Thank you very much!!

[estación seca]

Mine don't mind a week or so in the 5 degree range, but most of my winter has warmer days. Den. parishii can't take as much cold as the others you mentioned. I would try to keep it above 10 degrees.

[Roberta]

Those Dens can take nights a lot cooler than 10... mine experience winter nights as low as 4C or occasionally lower. But days are usually in the 15-20 C range. A few cooler days won't hurt, but if there's an extended period of cold days (more than a week), they probably need some protection. A dry orchid can tolerate temperatures a lot lower than a wet one. So if days are both cold and wet, that would raise the "rescue" basline temperature. If cold and bright (so surface temperature is higher than ambient) they'll tolerate more than cold and cloudy. So not a hard rule, and it is the extreme situations where you might have to intervene.

[Kittyfrex]

As roberta said. My D. nobile had live in even colder conditions, in full sun, with temps reaching very low negatives a couple of years back (not for prolongued periods, but it's worth to note). Made buds as if no ones buisniess. Just keep them out of harsh wind and rain (at least dendrobiums).

While i don't have many other dends, my nobile has started budding about two weeks ago, and my kinganium has made a new cane and some shoots from leaf nodes, that i currently have no idea if they are to be buds or some keiki kind of growth. One of it's hybrids i have as well had also made a growth and definitive two spikes (way too ball shaped to be a leaf on a shortish stem for now) AND two new canes.

They are full time outside, in half a days worth of sun (i would give them more, but it's not possible due to the layout of my yared and nearby houses) and mostly out of the rain, unless it blows from the south as it had yesterday. And as roberta knows, my temps had dipped the -1 (albeit for one hour before dawn).
Another thing she had reminded me of, that for some reason i didn't apply to orchids as well as other plants, is that you should consider both day and night as factors. If the days are warm, your plants will generally mind some nighttime dips far less than if it was cold overall.