dendrobium nobile: only grows keikis, no flowers

[headbanger333]

Hi there,
I have had my nobile for 2 yrs and, in spite of me withholding nitrogen and water over th winter, it is once again growing keikis only. I understand that this can happen if too much nitrogen is applied, but that is not the cause in this case. The 20 keikis were welcome last year as I ongrew them, but there is a limit and I really want the purple and white flowers. Any thoughts?
Cheers, Kathy