Could have something to do with the acid level in your soil? That also determines the color of the blooms. There are different types of hydrangeas too. Perhaps you have a variety that doesn't bloom a lot?
Is there any chance you could take a photograph of your hydrangea for us? Sometimes seeing the plant helps us to determine if there's an obvious problem. Could you also explain where it's situated in your garden? For example: in full sun, part shade. In a cool spot or hot area? Which plants do well beside it? Thanks that should help us quite a bit.
Pruning could be the problem. Do you cut your hydrangea back ever? Next years flowers are produced on the growing tips of this years growth so if you cut all of them off, you will dramatically reduce the number of flowers you have. I have worked in numerous gardens where the poor old hydrangea has been threatened with removal due to lack of flowers, and after I tell them the problem, and I sort it, the following year we have the reverse problem and the branches are weighed down by huge flowers.
Well, I can't take a photo RIGHT now, because it's ten o'clock at night, but it is in part sun, some grape hyacinths and dandelions growing next to it, and it's next to a pipe of some sort, I think. I'll try and post a photo tomorrow. I never cut it back.
Climate could be a factor, apparently... I found this link and within the body of the 1st paragraph of the text is another link called "Reasons Hydrangeas Won't Bloom." A cold snap after a warm spell and budding out can cause a problem with blooming. But it also says there are things you can doo to protect them. http://www.hydrangeashydrangeas.com/wha ... where.html
