If you want to obtain reliable bloomage from mopheads, you need to try several things: (1) remove dead wood in late May; if you have to prune for any other reason, only do so after they have bloomed but before July-ish... flower buds develop between July-August (August in the northern parts of the country) at the end of the stems so pruning in -for example- January would cut off the blooms for Spring 2017; (c) in northern cold climates, fertilize once in Spring only so the soil does not accumulate large amounts of nitrogen which makes hydrangeas develop nice, lush green leaves with few or no blooms; (d) transplant to get more sun if planted in dense shade (bright indirect shade is fine); winter protect in Zones 6 and less to get reliable bloomage by building a cage of chicken wire around the plant and packing it full of leaves, straw or mulch (really, really densely pack it if using leaves) such that you have several inches of leaves/mulch between the end of the stems and the "outside" or "top" of the cage. Remove the winter protection after all danger of late frosts has passed. (e) watch out for pests that like to eat the flower buds (deer, squirrels, bunnies, etc). (f) provide soil moisture as evenly as possible, make it moist not wet and definitely not dry for long periods of time, since periods of drought on/after July-August could cause the shrub to abort the flower buds. Adding 2-4" of mulch to the drip line or further can help with that.
Alternatively, grow in a pot and bring the pot into a garage or basement during winter (water every 2 or so weeks).
Some of the paniculatas I like are Limelight, Little Lime (more compact but blooms not as white as Limelight's), Pink Diamond, Quickfire, Little QF, Pinky Winky and either Strawberry Vanilla or Strawberry Sundae.
Have not tried a new mophead called Miss Saori that won a prize in Chelsea (just starting to appear on this side of the Atlantic):
https://www.rhs.org.uk/shows-e...
http://www.thompson-morgan.com...
