Hydrangea bouquets incorporate heavy flower heads that need extra support.
I've taped a long wire with light green florist's tape. This tacky tape (also sometimes referred to as corsage tape), needs to be stretched slightly as you pull it down the wire, twirling the wire with one hand while pulling the tape with the other hand. The light green tape blends in well and can be hidden among the hydrangea florets.
You "hook" the wire onto one of the support brackets of the cage covering the Oasis foam of the bouquet holder. I then threaded the wire through one of the heads of the lowest hydrangea stem of the cascade. You can then hook the other end of the wire on the other side of the bouquet holder.
The reason for this? To help support this heavy flower as it hangs from the bottom of the bouquet. Thread the taped wire down the cascade and through the laterals of the lowest hydrangea head.
An easier method than tape and wire is to use Floralock, a spray adhesive that is squirted around the stems after all flowers are inserted into the bouquet holder. It is easier and assures that no stems will slip out of the holder. Simply fit the red straw into the nozzle after shaking the can throughly and then making short bursts of the spray glue.
Do NOT squirt the adhesive until you are done designing, as it makes inserting other stems into the foam difficult once the glue covers the foam.
Now your cascading hydrangea bridal bouquet is well supported, secure and ready for the addition of the other flowers.