Harvey, my plant was in the shredded tree fern when it developed the sudden single-leaf yellowing, and I know from when I unpotted it that the medium was still faintly moist after 4 days (and it normally would be watered again in 3 more days). Nonetheless, the peripheral roots in the pot seemed dried out, so maybe you are right! I appreciate your warning about the new medium it's now in, particularly since its pot has side slits: I will water it more frequently. The humidity should be OK, as its saucer sits in a lake of water (no water in the saucer itself). Thanks!!! Sue

I'm going to make some wild guesses. I do not grow this orchid but looking at the roots and that leaf I have a few ideas.

Is it possible you are growing this plant too cold? If near a window, you are zone 6 and this orchid might need more heat to get going. Tree fern should be fine and drain quickly. The fact that it was still damp after four days suggests the roots are not taking up the water.

I do not see any signs of root growth. Roots should be starting to show signs of life.

The bulbs are shriveled. Those bulbs are losing moisture, thus the yellow leaf. They are getting nothing from the roots.

If it were my plant, I would increase warmth. Put it in the sunniest spot you have. If your room gets cool at night, I would move the orchid away from the window over night. Put it back in the morning.

Keep your lamps on all day for at least 16 hrs.

I may be wrong, but something is definitely going on. There is no sign of growth from the bulbs or the roots. Forget humidity, increase heat and light and see what happens.

Jane

I think you did the right thing by repotting into your preferred media, hopefully it will recover and start developing new leads. If possible get it outside where it is protected from mid-day sun, as you can't beat the real light. Always "ease" them out into the sun over a couple of weeks, they burn easily when first out. If staying inside, give as much natural and artificial light as possible.

I might also suggest to stop the soaking. Dunking is OK, but soaking for 1/2 hour each week seems to be an unnecessary PIA... FWIW: I grow indoors under lights over winter and my catts all get watered 1x week with a small watering can. When outside it is weekly with a hose (sometimes 2x week if it is very hot and dry), which provides much more water as opposed to the can. But I think they use more water when outside also, so it works out pretty well for me.

Good luck,

Bob

Bob, good info. But when you speak of watering I think it is important to explain your potting. If you use plastic with a lot of sphagnum or clay pots with lava rock, the required watering will be different.

On the dunking it also creates opportunity to pass along virus and other bad stuff.

Jane, it's in my sunniest location where often I need to run a fan to prevent overheating. My light is on for 14 1/2 hours. I will increase it to 16: thanks for that tip!

Bob and Harvey, thanks for more input on watering. One thing I did yesterday was to put the clay pot inside a glazed ceramic pot to help retain moisture. I will develop a new watering protocol for it.

Sue

Pot in a glazed pot is looking for trouble. Even the plastic pots have drainage holes. A general rule of thumb is orchids need to get wet and they need to dry to some degree or another depending on the plant. The 2 ways to adjust the moisture is the pot and the medium. Also involved in the calculus is your humidity and temps. I like the way you pot now. I think just increase the frequency of your watering. In their habitat, catts. are not in pots. Their roots are completely exposed. They live on trees or rocks. They get deluged by a short but very hard rain. Then it may clear to blue sky. And repeat. and sometimes repeat again and again. In general the best you can do is to mimic their habitat. To some degree. You can't bottle Costa Rica. And the good news is the orchids respond at partial efforts of trying to mimic their habitat...

Culture notes. I read a few culture notes and they seem to agree... http://www.orchidflowerhq.com/Cattleya-warscewiczii.php 

OK, no glazed outer pot; just more frequent watering, allowing to dry in between. Thanks! Sue