| For Cattleyas, in general, I say nothing below 40F for very long. Ideally, 48 would be the low, but down to the low 40's and even upper 30s won't kill the plants, just slow them down. I'm keeping the GH around 50-55 as a low, right now, but it also hasn't gotten below 35 outside. WHen it hits the upper 20's, as it will likely do a couple of times this winter, I'll make 42-ish my minimum.
Also, a one-night dip below ideal temps will not kill a plant, unless it is freezing, and as long as the day temps get back to an acceptable range, the plant shouldn't miss a beat. You might blast buds, playing the odds that way, but you are not really likely to severly hinder a plant, as long as all other aspects of the culture are alright.
-Cj |