Whether or not to prune your Hydrangeas — and how to prune them — is one of the most common questions our service department receives. We’ll try to simplify the answer for you below.
Old wood or New wood?
Hydrangeas can be grouped into two categories—those that produce flowers from old wood (branches that form the previous season), and those that will flower from new wood (branches that form the same year). Easy, right? Not so easy if you’re not a horticulturist. So we’ll simplify things a little. Fortunately, nearly all of the hydrangeas that produce white or whitish flowers fall into the new wood category, and those that are pink-to-red or purple-to-blue (depending on how acidic or lime-based your soil is) flower on old wood. Not to confuse the issue, but the hot new variety on the market, ‘Endless Summer’, blooms on both old and new wood and comes in both white and pink. We’ll lean towards the ‘New wood’ category on that one.
New Wood (white flowers)
You can cut them down to the ground each spring and they’ll give you great flowers the same year. If they happen to grow like a tree, then cutting them back hard without losing their tree-like characteristics will work just fine.
Old Wood (pink-red to purple-blue flowers)
Thin them out in early spring by removing the obviously dead stalks. You can reduce their overall height if desired by cutting off the top 12” or so of the remaining stalks, making sure some live buds remain along the sides of the stalks. Note: after a severe winter, all buds might be killed, despite your best efforts. In this case, you won’t see any flowers at all that growing season.