Climbing hydrangea with twisted leaves

(Question)

Zone 8A, shady location, average moisture site, sandy soil.
I have had my climbing hydrangea for eight years. It would probably like a bit more sun, as it is on the east side of my house and the neighbor’s house blocks the sun, but it has been a healthy plant, though not very many blossoms. This is the third year that it pushes out healthy leaves in the spring, and then they suddenly they all get twisted and stuck together. It’s almost as if they grow like crazy and can’t unfurl, and if I try to open up a cluster of leaves they are damaged. I’m thinking of trimming the plant way back this fall and giving it one more season before digging it out. Any help or suggestions is much appreciated.

(Answer)

Climbing Hydrangea, Hydrangea anomala ssp. Petiolaris, is generally tolerant of shady conditions, and is considered to be disease-resistant.  However, there are some insect pests that can cause the damage that you describe.

Aphids, which are small, soft-bodied sucking insects, cluster on new shoots and leaves and suck the sap from the plant.  They can slow down plant growth, and can cause leaves to curl up.  You should be able to see them.  They can be removed by spraying forcefully with water every day or two.  Spraying with insecticidal soap every couple of days is also recommended.

From your description, another possibility is the hydrangea leaftier (Exartema ferriferanum), a small moth that lays its eggs in the branches.  When the caterpillars hatch, they curl leaves together, tying them closely with silk thread to form an enclosure in which they feed until they pupate.  Here is a previous Toronto Master Gardeners post that describes this insect, includes a very good clear photo, and provides advice on care:

https://www.torontomastergardeners.ca/askagardener/hydrangea-leaf-curl-with-worm-inside/

It shouldn’t be necessary to trim your climbing Hydrangea back in the fall, but do make sure that you clean up any leaf debris around the base of your plant when you are doing your fall garden clean-up.