Question for Florists

I would really like to make little bud vases serve as place holders and also an additional guest favor. Of course the bud vases need a bud in them. If I purchase the vases, what do I do with the florist - do I give the vases to the florist in advance? Does the florist just bring the flowers to the reception hall and put them in there? What's the protocol on this?
Thanks so much for your help!

Janice