Hello…this spring we planted a Limelight Hydrangea Standard .. it absolutely thrived and we love it .. large flowers too. Unfortunately part way through the summer the limbs splayed to the point that I had to stake the limbs to keep the flowers somewhat upright. It looks rather odd but the flowers are plentiful and large and the leaves look great. Any thoughts on what may have happened and how to prevent this from happening again? Thank you very much for your help.
Thank you for contacting the Toronto Master Gardeners.
The standard hydrangea that you have H. paniculata ‘Limelight’ has a tendency to flop and split under the weight of their blooms. If you are not a fan of the flopping branches, changing your pruning habits can encourage studier stems. This type of hydrangea produces flowers on branches that are produced the same season ( known as new wood). This means that you can cut the branches back in the fall, winter or in early spring, when you can see the new buds.
The idea is to shorten each branch to about 2-3 sets of nodes each. These are the little bumps that become side shoots that eventually produce the buds that flower later in the summer.
When you prune a branch back more shoots will grow below the cut, making the plant more dense. This practice is called heading back. If there are two buds opposite each other below the cut then remove one. If you let both buds grow, they will form a forked, weak stem.
If you don’t shorten the branches, they grow too long and the plant arches out and down too much. Sometimes they even snap off from the weight of too many big flowers on the tips. Shortening also forces flowers to happen closer to the main branches so all your blooms aren’t on the tips of long shoots, this kind of severe cutback makes a nicer, more compact and sturdier plant later in the season.
The last thing is to snip off any stragglers that want to grow straight up or inward. Cut those back to the trunk or to one of the main branches if it’s attached to one of them. You don’t want a branch to jut up or any to be growing inward toward the opposite side. The goal is that nice umbrella where all the branches are arching out gently all around from a point about 4 feet up on a bare trunk.
Here’s a link to a very good website, all about hydrangeas, including pruning tips and photos.
https://www.hydrangeashydrangeas.com/pruning.html