productive pots

I have the opportunity to sell potted iris at an enormous garden festival next May, about two weeks before my peak bloom for the field plants.

I have about six hundred iris potted. They are currently in an unheated greenhouse, soaking up a few last warm days of sun. They might winter in there - I'm in there several times a week and can keep an eye on them. I've wintered some pots in there in the past - just not so many.

In the past, though, I haven't cared so much about when the potted iris will bloom. I know I can manipulate the temps a bit in the spring to slow them down or speed them up if necessary, but I'm wondering about the timing of fertilizer in the spring. I'd like to go to the festival with as many in bloom as possible. Has anyone potted iris with the goal of bloom on a certain date, and what hints can you share?

katie