[mdjlucan]

When do I prune this and straighten it out


Edit to clarify title

[mrs bouquet]

I would put some supports around it to lift of the grass, and then leave it so that you can enjoy the flowers, they are nice in winter when they get a glint of frost on them.    Cut back in spring.   It looks as if your space for it might be a bit narrow, could you cut some of the lawn out to let the Hydrangea have more space.  It may have flopped because it is dry, or trying to lean to the light.   Good luck.   Mrs Bouquet

[mumofstig]

The flowers are usually left on until spring, because they give some protection to next years growth buds.
As Mrs B says put some sticks around it to hold the flowers up, the bushes grow quite big, so maybe it's not in the best place