My Zygopetalum leaves are turning yellow, then brown. What can I do?
Both my plants are 'rescues'. They put out new roots & pseudobulbs/ leaves, but never a flower spike. More recently they are losing leaves. I have re-potted them and the roots look good. One is in a western exposure window and the other in a shaded southern window. They are potted in a combination of small bark and moss. 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 and the humidity is in the range of 30-60%. I fertilize "weakly weekly". Can you offer any suggestions?
Answer
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 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.
Courtesy of NYBG Plant Information Service
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