Tim,

I'm no pollen expert, but one of my colleagues is. I
posed your question to him and he says that while the answer is extremely
species-specific, people have had success storing dessicated lilly pollen at
-80o for extended periods of time. Hope this works for
you.

-Greg

Thanks Greg, a peek at the other 2 threads with the same title will give you
a clue as to the species I am interested in, however, unfortunately I'm afraid that -80 is a tad cooler than my freezer can manage. But thanks for taking the trouble to reply anyway.