My hedge overhangs property line. Who is responsible for neighbors side?

Basically the owner of the hedge is but if the property owner of the side where the hedge is growing over the property line gets tired of looking at this mess he may legally trim the overhanging hedge with no repercussions legally from the hedge owner.

Your neighbor CAN cut it if he wants or, being a good neighbor, you could cut it. Anything across the line is basically the persons whose space is encroached. For example, if it was a fruit tree and all the fruit was on you neighbors side, and his property, he could take all the fruit.