I would suggest that you give a florist the task of making sure that the hydrangea flowers will be good and ready. Macrophyllas will begin to bloom in May here so no problem there but, there are many things that can happen so give the florist the task and cross that item from the list of things to do.

Agreed - check with a florist. Shrubs in the ground around here (sort of equivalent to Austin) are starting to bloom already (well, mine are). Hothouse hydrangeas were being sold in full-bloom at the big box stores in February, so it should be easy enough to obtain, just ask around.

If you have an Aldi's in your area, they had them last week for $4.99. You'd just have to keep them looking good until the wedding. Congratulations on your big day--we are doing my daughter's outdoor wedding in our yard in September. SOOO much work to do!!
Best wishes!
Karen