Hydrangeas are a fan favorite around here and knowing when, how and whether to prune them will have them looking their best year after year - if you follow a couple of rules to remember.
If your hydrangea is just blooming now in late summer/fall, put it on your calendar to prune it in late winter or early spring. This time frame is appropriate for Limelight, Quickfire, Burgundy Lace and Annabelle hydrangeas (which is the classic "snowball" type). PeeGee hydrangeas - which produce creamy white flowers in late summer that age to rosy pink - are also in this category. These varieties bloom on new wood, meaning the blooms come on stems that grow new each year.
Other hydrangeas bloom on what is called “old wood,” meaning the buds for next year’s flowers are set on the growth that happened this season. This occurs with oakleaf and bigleaf hydrangeas, lace caps, climbing and all varieties that bloom blue or pink - like endless summer and summer crush - among others. You should prune these types before August… so not again more this year.
But the bottom line is... unless you need to control the size or shape of your hydrangea, you don’t NEED to prune at all. If you choose to prune, cutting out the oldest, biggest canes will help to control the size and can reinvigorate the shrub.
To get bigger flowers, cut them all the way back to the ground, but also consider that leaving some stems 18” to 24” high. That can help reduce flopping next year.