Carianne,
Whenever we do a cascade, I always use the large bouq. holder. We cover the back with glued on fresh ivy leaves and tape rose stems (we have saved in the cooler) around the plastic handle for a natural bouquet look, but having the safety of a wet foam holder.
Is the entire bouquet All Hydrangeas? If it is, were you going to cut and piece the hydrangea florets to trailing ivy for the cascade? If not, what flowers were you using for the cascade?
I have used pcs of hydrangeas with a rose for a bout. and I sprayed them with crowning glory and they were crisp the next day for the wedding. Another time, the hydrangea part of the bout shriveled and I had to add a fresh hydrangea to the rose bout.
I don't even recommend this to the brides. I would only do this type of bout the night before the event.
Marie