Not sure about the mane growth as I pull mine quite short, but for tails I highly recommend bathing the tail then wrap it using the vet wrap method (link below). Before you wrap it I'd put some cowboy magic in as well, and then the top part, like the tail bone, MTG.
I wrap both my mares tails as they both had baby tails that came to about hock area or a few inches about at one point. I have been wrapping them now for 7-8 months and both their tails are fetlock length. I re-wash/wrap every 2-3 months.
Sorry, I had a much better link at one point but can't seem to find it now so this is the best I can find..maybe someone else will know of a better video.