Mophead hydrangea blooms pink in alkaline soils and blue in acidic soils. Blooms spring and re-blooms summer to fall.
The best advice is to keep in mind (before planting) how big the shrub will be at maturity. Space your shrub away from your home a little over 1/2 the spread length. For instance: if your mature spread is 6' then plant it (at least) 4' from the base of your home.
PRUNING HYDRANGEA MACROPHYLLA:
Bigleaf hydrangeas set their flower buds at the ends of the upright or lateral branches, during late summer to early fall. Pruning Bigleaf hydrangea in the spring or even late fall, after the buds have been set, will remove the flower buds and any chance of getting flowers that season.
Bigleaf hydrangea should be pruned as soon as the flowers have faded. You should begin to see new growth coming in from the base of the plant, about this time. To keep the plant vigorous, selectively prune out the dead and weaker stems, both old and new. Don’t prune out all the old wood, since this is what will keep flowering as the new growth matures.
Bigleaf hydrangeas are the variety most susceptible to winter bud injury.