Hydrangea serrata 'Blue Billow'

Nice ,looks very compact is that due to pruning

mum had a hydrangea that was part blue on one side because there were nails buried in the ground under it - she said that was the only way to get blue flowers on them, but you've proved her wrong

This hydrangea is more compact but I don't usually prune it. I have grown a few from cuttings and will cut off dead stems in Spring but mostly I leave hydrangeas alone. Most of them have the top 1/4 to top 1/2 die back during winter because they are not fully hardy here. The buds covered in mulch or snow survive and that is it. This is by far the hardiest hydrangea I grow and I have never seen die-back on it.
The reason it is blue is I have treated it with Aluminum sulfate to acidify the soil and make sure there is Aluminum available. I treated it last year and probably won't have to do it again for a while. Hydrangeas need Aluminum for blue flowers, making the soil acidic makes it possible for the plant to use Aluminum.