Usage patterns
髪を染めるto dye one's hair
髪を伸ばすto grow one's hair long
I've been growing my hair out lately.
髪を洗うto wash one's hair
I washed my hair before going to bed.
髪をまとめるto tie up/put up one's hair
I tie up my hair when I exercise.
髪が伸びるfor hair to grow (long)
Children's hair grows quickly.