Q. Zygopetalum Leaves Turning Yellow, Then Brown
I have had 2 Zygos with a couple of pseudobulbs each for a couple of years. Both were considered 'rescues' when I got them. Initially I had success getting them to put out new roots & pseudobulbs/leaves, but never a flower spike. I assumed that they were still in recovery mode and might not flower for a year or two. More recently they have made a turn for the worse - leaf loss. I have repotted both of them and the roots look quite good. One sits in a western exposure window and the other in a shaded southern window. They are potted in a combination of small bark (75%) and moss (25%). I water them thoroughly once per week and spray the surface and visible roots in between. The temperatures in my home are 65-75°F (~5°F cooler in the winter) and the humidity is in the range of 30-60%. I use 75% rain water and 25% tap water (~200ppm TDS), fertilize "weakly weekly" with Orchid Plus, periodically supplement with Ca/Mg and flush once per month. Neither plant appears to have any insect infestation. From everything I've read, my conditions are at least in the ball park to be successful. The reality is that I need to change something. Can you offer any suggestions? Thank you for your assistance, Jack
Thank you for getting in touch Jack. I'm sorry to hear about the problems you are having with your orchids.
It sounds as though your zygopetalums may be experiencing too much moisture in both their growing medium and their environment. These orchids are epiphytes and very intolerant of a planting mixture that does not drain freely. Whereas the moss in your planting mix would be ideal for many orchids, zygopetalums are better in a fast draining mix such as bark and perlite. For the same reason, they also do not like a traditional, deep orchid pot and prefer something far shallower.
Your day temperatures sound fine though a drop of ten degrees or so at night is ideal. The humidity is running a little high for these mid-temperature range orchids. Around 40% is better and higher than that will start to damage the leaves.
Finally, check that their location is giving them the classic bright but indirect light they prefer. All sorts of things like tree shade, curtains, nearby buildings, can affect the degree of light available regardless of the exposure, but direct southern and western light may be too intense.
Let us know if we can offer further help.
With best regards,