What kind of Hydrangea is this? When to prune and how far do I prune back?...
Your hydrangea is a paniculata, possibly a variety called 'Limelight.' It blooms on new growth each year and should be pruned late fall when the plant goes dormant or early spring before it gets new leaves. LW
How far back on the stem do I prune it?
It is generally recommended not to prune any more than 1/3 of the shrub at any time.