Snowball, or smooth hydrangea (Hydrangea arborescens) prefers rich, well-drained soil that stays consistently moist. It does best with morning sun and afternoon shade, or dappled shade all day. The more cool morning sun it gets, the better it blooms. If you have provided your plant with these growing conditions, it might still be adapting to its new location and putting more energy into root growth than flower production. You may see flowers next year.
Excessive nitrogen fertilizer or improper pruning can also cause a lack of flowers. Snowball hydrangea blooms on new wood, so pruning in late spring or early summer will remove potential flowers. Is it possible that the plant you picked up is a different type of hydrangea. Bigleaf hydrangea (H. macro-phylla) is less hardy than snowball hydrangea. In Zone 5 or colder, its flower buds are often killed, but it will still put out new vegetative growth.