Q: That raises the question: Should I be pruning at all?
A: If your hydrangeas are sited correctly, with enough room to grow, the only pruning required is to remove dead wood—be sure to take it off at the base of the plant if the whole branch is dead—and spent flowers. In Dirr's experience, all hydrangeas benefit from regular dead-heading to encourage more blooms. Left unpruned, they will produce fewer flowers because of a growth-inhibiting chemical released by the terminal bud at the tip of the stem. Don't prune past August, though, because any new growth is susceptible to an early-fall freeze.
"Whether to prune hydrangeas is often debated, but studies have shown that dead-heading spent flowers definitely encourages more and bigger blooms," say horticulturalist Michael Dirr.
Shown: TOH landscape contractor Roger Cook clips large flowers from a mature peegee. These tree-like shrubs reach up to 25 feet tall, with white to pink conical-shaped, mid-to-late-summer blooms.