August 1st is the unofficial "last day to prune" mophead and lacecap hydrangeas. These "big leaf" varieties bloom on old wood and begin setting their buds as early as late August. A fall prune will result in no blooms next spring.
Don't know what variety you have? A good rule of thumb is that if it is blue, it needs to be pruned in the summer. Same goes for shade loving. Most shade loving hydrangeas are big leaf varieties.
Newer reblooming big leaf varieties like Endless Summer and Let's Dance are cultivars and they bloom on old wood and new wood. You can "get away" with pruning these varieties in late winter ... I'd still recommend pruning in late July or early August for the best show next Spring.
As always... Akin's is here to help!
