Smooth hydrangeas tend to suffer from flopping issues once their large blooms make the stem "top heavy" and summer storms/winds visit. They should always be aided with stakes, peony hoops and-or tomato cages. These tools should be revisited annually once the plants drop their foliage so you can tweak as necessary before spring arrives. Pruning of stems will promote flopping as new, green stem growth is weaker but woody looking stems are stronger. There are some varieties that advertise stronger stems like Incrediball and Invincibelle but take it with a huge grain of salt. As mine and others have done, these varieties are slightly stronger but are not immune to flopping. They too will flop if the right storm hits. Annual tweaks of the tools to prop them is useful as the shrubs tend to propagate via suckers; however, I gained some form of control by cutting off the suckers in spring.
