I have a Hydrangea that I believe I have over fed. It has a massive amount of leafy growth and very few flowers.
Is there anything I can do to restore the balance?
You can also use a tomato food which promotes flowers rather than foliage. Or any feed with higher potassium/potash content if you can't get comfrey as Alan suggests. Not sure it'll have any great effect this year though Julie as Hydrangeas are busy flowering now so might be as well to wait for next year.
I suppose you didn't prune it this year? Hydrangeas flower on last year's wood. I've made that mistake myself in the past.
I've had the same problem. No flowers last year either, so I gave a very light prune early in spring, also fed tomorite - still nothing except very healthy leaf growth. Been advised bonemeal may help - oh well I'll try !