Question
I recently bought some from the local market and I have a south-facing window.  However, I noticed all started to have leaves turning yellow.  They are a good couple feet away from the window.  What am I doing wrong?

Answer
It is likely that your dendrobiums are telling you that they are going into a rest period.  During that period, they do not put out new growth. Yellowing and loss of leaves is typical of dormancy.  If you try to water these plants when they are not in growth, there is a very strong likelihood they will die. You might lightly mist them but water should be withheld until there are signs of new growth.  The misting would be to help prevent dessication of the canes.  So, if you see them shriveling from lack of moisture, mist them lightly each morning.  Otherwise, they need to be left to rest in peace.