Originally Posted by
mauraec
I'm NOT an expert in this area, but I wonder about a few things. First, orchids in general need that drop in temp at night in order to induce new growth, spikes, etc - we try to mimic their natural surroundings, and warming their water (and having that heat transferred to the hydroton as a result), especially at so great an amount of temp rise, seems to me to be a little shocking to the entire plant system. I've never used warming mats, but I would think they'd be providing a gentler rise in temperature. S/H aside, I also am concerned that your orchids (and it looks like you've got 3 phals in S/H, one in water, and an oncid of some kind in S/H) might not be getting their minimum preferred temperatures at all. Phals are generally warm-growers, and prefer 65F/18.3C as a night minimum. During the day, they prefer a 15F rise in temps and so on. So, I think your phals might be a tad cold, as is, and then raising the temps so much from below is going to leave them too cold on top and too warm below - in my experience, a recipe for root rot. Oncids can go down to 55F/12.8C at night.
From your post, I gather that the inside temp of your apt is 55F??? Isn't that a bit chilly for humans, never mind orchids? And you put them outside where it's about 43F and they're in shade (bright, I know) most of the day? Have you had them for a long time in this environment? Maybe they've acclimated to it, but it's really overall pretty cool for orchids - except for the real cool-lovers, like cymbidiums, some masdevallias, miltonias - and it still might be a bit cool for them. And judging by the deep green color of the phal leaves, they're not getting enough light. Phals ARE low-light plants, which is why a bright east-facing window is good for them, but the plants will tell you what's going on, anyway. One of the easiest signs to recognize is deep green leaves (not good for orchids) - very pretty, granted, but generally reserved for houseplants that don't flower.
Of course, if your plants have been flourishing, ignore all this advice.
I have gradually transplanted nearly all my orchids, including phals and oncids, into S/H in the past 2 months. Aside from making sure they get the light, temps, nutrition, and water they need, they're on their own to develop roots for S/H purposes. In other words, I'm still growing them the same way I did before, and so far I haven't lost any. Remember though, S/H is not a magic solution - all the other growing requirements apply still, and I still may lose some of my orchids - it just works out that way sometimes. But I'm pretty leery of heating them from the bottom - it's a bit like the equivalent of watering them with fairly hot water.
Just my own thoughts - your idea about warming mats certainly applies to germinating seeds, so gentle warming from below may help. Good luck and let us know how it turns out!