I assume you mean "peegee" hydrangea. Several questions--is the plant in full or nearly full sun? It does best in full sun. In any case, a peegee hydrangea blooms on new wood, so the best time to prune the branches is in spring. Fall pruning encourages shoot growth, the shoots are usually too weak to survive winter, and the entire plant will suffer from putting it's resources into new growth instead of into it's root system. But you can pick off just the blooms now if you like. I usually but the stems of peegees at the peak of their blooming,just when they begin to get a pink blush(August in Minnesota), hang them upside down in a dark, warm and dry place, and they last for years as spectacular dried arrangement. Another thing, most perennials have an "off" year once in awhile. Not to worry if you don't get the same performance from your plants every year--they're living things, and all us living things have our ups and downs.