Q.Thank You. I Have , What I Think Are Mophead Hydrangeas. Done Well In This Location For Years But I Didn’t Prune Correctly. Now The
y are quite lanky and tall and no blooms. How should I prune them this fall to promote blooms They are shoulder height now with very few blooms in the past two years. I don’t know how to prune them. Should I cut way back to a low height or at certain points on the stems?

Certified GKH Gardening Expert
Mopheads can be pruned AFTER they bloom. It's too late now to prune because they already have formed buds for next spring. Here is more:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/mophead-hydrangea-care.htm