There is a very good chance a florists hydrangea may not be winter hardy in your zone - I assume this is macrophylla, the mop head type?

Understand that these have been given extremes in conditioning and care, subjected to fertilizers, controlled lighting and temps , sometimes plant hormones to bring them to bloom coinciding with a particular holiday, not with regard to long term plant health.

You can harden it off gradually to get it used to weather and wind, plant it, see what it does. In this 8b the florists types will sometimes thrive and do quite well, providing years of vigorous blooms, but even here it can be hit or miss with no guarantee.