Question
I have made several crosses and each time (so far) the flower has closed around the pollen and within a couple of days the stem behind the flower turns yellow and falls off. The rest of the spike is green. This has happened with a miltonia, a now with two brassias, and a dendrobium. The plants are thriving and producing new leaves and shoots and the roots are good. We have had a lot of foggy mornings with temperatures in the 50s and them arming to 60+ degrees. They are not in direct sunlight and I water when they are dry. I bought these plant and I have no idea how old the flowers are could that be the problem?
Help?
Dan Turner

Answer
Dan, for new crosses, the first flowerings are usually weak and, frequently do not mature properly.  Future flowering on well grown plants should be better.  Plants that are purchsed in flower may appear to have a premature end to their flowering when, as you suggested, these flowers may have been open for some time and sre reaching normal senescence.  Finally, there are  environmental factors that affect flowering, as you have suggested. Buds and flowers are very sensitive to temperature.  I would be especially concerned about temperatures below 60 degrees or above 85 degrees.