Since my name was mentioned, I thought I'd drop in. Was out of town until Monday late and have just barely caught up on other things around the house. I don't grow in a greenhouse, but if I had to I would not dry them out in winter or anytime. Situate them so that they are protected from the highest heat, I think they start failing at 95 F or so. Shade in summer to avoid excess heat. Sun on a plastic pot can cook roots, so set the armeniacum pot into a taller and larger diameter clay pot. Leave the void between the armeniacum pot and the clay pot empty. The air space provides insulation. The clay pot should be tall enough that the sun can not shine directly on the plastic pot. This will help keep the roots from being overheated by the sun. Those are my thoughts on greenhouse growing.
I will add how I grow armeniacum, because maybe you will see 'the trick' or the difference between what I do and what your greenhouse does.
I have a room that grows armeniacum beautifully. I have some 10 or 15 different clones, at least 4 I have kept alive for over 20 years. One I picked up in 1987. So I guess I have a little experience.
While I keep them alive, they do take their time about blooming. I would say most of mine take 4 or 5 years to mature a growth and bloom at the quickest. Single growth plants can poke along for a decade without blooming. Virtually 100% of my armeniacum are divisions of originally collected material, none of mine are from seed. I do have divisions of 2 different awarded armeniacums, some of the collected clones are very nice. All are at least charming.
I grow under lights in a basement. For armeniacum I keep it in the brightest region (directly under in the middle of the shelf), of the light stand with T5's in my 'cold room'. This room is a former coal cellar, no heat ducts in this room. Bare concrete floors and concrete walls. So the humidity is up and the temps are cool compared to the rest of the basement. In winter it can get as cool as 55 F or roughly 13 C. Which is not that cold, more an intermediate temperature. During the day in winter, when the lights are on, the heat of the T5's does bring the temperature up at least 10 F (up about 6 C). I grow my micranthum in the same room, but on a shelf with T12 shop lights, so the light is less than the intensity that the armeniacums are getting. Lights are on 18 hours per day, 365/yr.
In summer this room gets warmer, as the house does not have central air conditioning. But since it is a basement, it rarely gets over 90 F (32 C). In summer it does not cool down as nicely as I would like it to. This year in particular night time temps were over 80 F (26 C) for at least one month. This is bad for cool growing orchids, the armeniacum and micranthum did not seem to mind, I would not class them as cool growers. They tolerate cool, they don't need it the way a Masdevallia might. Look at their home climate, warm wet, rainy summers, with August being particularly warm, even at night. Cool and somewhat dry winters, but remember, these are mountain plants, they might not get daily rain in winter, but they do get fog, or dew, this condensation can be substantial, and would keep the mosses and soils they grow in at least lightly damp all winter, even if there is no rain.
A couple things I do that I think help. I use as small a pot as I can get away with, most of my armeniacums are 1 to 3 growths in 2.5 x 2.5 x 4 inch tall pots. I try to repot at least once every 2 years. If you rot the roots off, it takes forever to put roots back on. Best for me is to repot once a year, but that doesn't always happen. Never delay repotting so long the mix breaks down. Sometimes I grow directly in Yi-Xing pots, just to be 'artsy'. Have a division of armeniacum 'Birchwood' FCC/AOS growing in a basket with nothing but New Zealand Sphagnum moss. It was a small single growth fragment with no roots, now leaf span is about 7 inches, and a new growth is peaking up near the edge of the basket. If I had the room, I would put more paphs in baskets, but they don't work well under lights for mechanical/logistical reasons.
I do not dry them out in winter. They seem to do best if you keep the mix lightly damp, and water again before it goes to dry. I don't keep them wet. The tall pots hold less water than a wider & shorter pot. The mix doesn't stay too wet.
I use a fine mix, particle size between 1/8th and 1/2 inch. I use a hardware cloth screen to eliminate big particles, and a coarse window screen to eliminate the fines. My mix is roughly 2 parts fir bark, 1 part coconut husk chunks, 1 part perlite and 1 part charcoal. I sift / shake over the screens, then mix the components, then add enough water to wet the mix. Then I add roughly 1/4 part sand, fine play sand or pool filter sand. Mix it up, let it stand over night and mix again. The sand will stick to the particles. This is my general mix. As I repot, the lime loving species get a tablespoon or so sprinkled on top of their mix of crushed oystershell and/or horticultural grade lime, I don't mix this in, just let it sit on top. Then I water them and put them back under the lights. (sand is from suggestion by Ernie Gemeinhart, and I get real nice roots, especially on my brachys)
I'm using MSU fertilizer at 1/4 teaspoon per gallon continuously, every time I water. This is about 75 ppm as Nitrogen. I plant to switch to K-Lite as soon as I use up the 25 lbs bag of regular MSU that I bought last year. It is almost gone. Yes, I have enough plants that I do use 20 to 25 pounds a year of fertilizer.
That's it, no tricks really. They grow for me, though they definitely are slower than most species. This is the reason I have so many clones of armeniacum. Since they are so slow, by having 10 or 15 of them I do get to see one or two bloom every year. So the solution to slow growing plants is get a bunch of them. :evil: Easy with armeniacum & micranthum, but you would need a lot of space if you were to do this with stonei or sanderianum.
