The "Nikko Blue" variety of Big-leaved Hydrangea grows about 4' tall in my garden.  It begins blooming in mid- to late June.  Blue varieties of Hydrangea require an acid soil to keep the flowers blue.  (Red and pink-flowered varieties of hydrangea only require a slightly acidic soil).  I put aluminum sulfate around mine each spring to acidify the soil.  The best place to plant your Hydrangea is in partial shade.  If you plant it in full sun as mine is, it will wilt during hot weather.  The best way to prune a mature Hydrangea is to cut the flowering stems all the way back right after the flowers have faded.  The non-flowering stems will produce next year's flowers.  This might sound drastic, but the plant will be just as full the following year.  Hydrangeas can be propagated by letting a low stem lay on the ground (putting a heavy rock on it helps).  It will form roots where the stem comes in contact with the ground.  Another way of propagating it is to just break off a good chunk with a shovel.