Keep it in plaits over the winter and only re do them every couple of weeks. This helps the hair grow longer and thicker. If you want to make your horses tail longer plait it from the bottom of the dock down, and if your horse is scratching it out try lubing up his/her bum and worming. If it’s not worms, leave it plaited and put coconut oil or honey heel on it daily.
Do not cut it or shave it at the top as this is where the tail grows from. Coconut oil is very good and don’t brush it as it pulls out the mane and tail
I've heard that coconut oil works
Apply coconut oil to the roots of the mane and tail in the evening
don't brush it as much so you don't pull any hairs