Cut hydrangea bunches into single stems using a sharp knife or florist's scissors.
Trim the hydrangea stems to fit the vessel you are using to hold the flower arrangement. Snip the stems at angles to ensure maximum water absorption when the blooms are resting in the vase. Vary the stems' lengths by 1/2-inch increments to create an interesting arrangement.
Separate the hydrangea stems by flower color before creating the arrangement. Create an all-pink or all-blue floral arrangement, or use a combination of colors. Place one blue hydrangea in the center of the vase and surround it with pink flowers, or design an arrangement using two pink, two white and two blue hydrangeas as another option.
Place the cut hydrangea stems into a water-filled vase immediately to keep the flowers fresh.