How long does it take for manes and tails to grow back?

How long does it take for manes and tails to grow back? Say a mane was roached, or a good portion of a tail was cut (an inch or so below the tail bone), how long would each situation take to grow back?

I'm not absolutely positive. I've had Wes almost 5 months, and when I got him, I cut a really good portion of both is mane and tail off because they were disgusting, and I just recently had to do it again. It all depends on the horse I'd think.