Perhaps it is a pathogen problem. I examined your photos closely. Do you spray the plants leaves with water as well. If so you may have got yourself some nasty erwinnia germs. Otherwise try to hang the vanda's in the open air freely. Somehow the roots like that much more. Did you meassure your temps exactly? Maybe your temps are dropping way below 10 C at night. Everything below 10 is getting critical. I used to table temps like this:
50 C - Critical temp, watering won't help you any longer
40 C - Adjust before its too late
30 C - water alot and let nature do the rest
25 C - I understood that this is the tropical temp thus ideal
20 C - Near ideal, water and enjoy
15 C - Try heating up a little, plant will grow roots and new leaves
10 C - Plant stops growing and will start trowing leaves if exposed too long (like 2-3 weeks)
5 C - critical temp, exposure longer then 4 hours will damage roots and leaves and eventually kill the plant
<5 C - Immedate death. No rescue possible
Now this is comming from my experiences with a variety of plants. I may be wrong about it. So far my vanda is still alive but anything can still happen
Your phalas should be immortal so they are simply overwattered or in the wrong substrate. I never have seen a phala die and I have seen them bloom at conditions even my cacti would die in.
Anyone correct if Im talking crap. I am still learning after all those years. Hope this info helps
Phalaenopsis Dalmatian and Vandas
Linear Mode
