Ok, I have a bunch of bushes that go along my driveway. I m 42 years old and I planted one when I was 2 years old and that's the newest one. They probably have not been cut back or taken care of for 15 years or so. They are in desperate need of some TLC. My question is how far back is it safe to cut them back? I don't want to kill them I want to try and save them and be healthy.