First find out which species of Hydrangea you have by researching your cultivar's species.
For example: Hydrangea 'Limelight' is paniculata and 'Endless Summer' is macrophylla.
Hydrangea macrophylla and Hydrangea serrata
Prune in late winter or early spring after growth resumes - remove dead wood back to just above live buds.
If stems have been persistant for many years thin to rejuvenate by removing 1/4 to 1/3 of oldest stems back to base.
Following harsh winters the entire plant may need to be taken back to just above the soil level.
Most cultivars will not flower on new wood. Flowers should resume next year if winter is not too harsh.
Macrophyllas prefer morning sun and afternoon shade. They'll require more moisture depending on sun exposure.
Flower color can be altered depending on soil. Soil with a pH below 5.5 typically produce pink, rose or red flowers.
Blue pigment is dependent on available Aluminum in soil. To attain serious blue adjust soil pH accordingly and
add aluminum sulfate according to supplier's instruction.
Blooms on new wood - easy maintenance - can be pruned to ground in late winter before new growth begins.
Can be thinned out by removing 2 year old stems and leaving recent years growth. Leaving some woody structure
can help prevent plants from flopping.
Tolerates full sun to deep shade although it blooms best with more sun exposure and moist soil.
Prune only to shape or remove dead branches - avoid the need to prune by choosing the appropriate cultivar.
Tolerates full sun to part shade, drought stress diminishes flower color and longevity of show.
Blooms on new wood, can be coppiced (cut completely back to ground or stump) or pollarded to great effect.
Performs best in full sun or light shade.
Prune only to shape or remove dead branches after it blooms.
Performs best with even soil moisture and in bright light with protection from hot afternoon sun.
Gardeners' Voices: Hydrangeas
Dan Benarcik and Jonathan Wright
Woody Plant Conference July 2014 - The Scott Arboretum