I had a look to see what Tacitus had to say about this in "De origine et situ Germanorum liber". Hairstyle comes up twice, once in 31 and once in 38.

31 is about the Chatti: (31) A practice, rare among the other German tribes, and simply characteristic of individual prowess, has become general among the Chatti, of letting the hair and beard grow as soon as they have attained manhood, and not till they have slain a foe laying aside that peculiar aspect which devotes and pledges them to valour.

About the Suevi: (38) A national peculiarity with them is to twist their hair back, and fasten it in a knot This distinguishes the Suevi from the other Germans, as it also does their own freeborn from their slaves. With other tribes, either from some connection with the Suevic race, or, as often happens, from imitation, the practice is an occasional one, and restricted to youth. The Suevi, till their heads are grey, affect the fashion of drawing back their unkempt locks, and often they are knotted on the very top of the head. The chiefs have a more elaborate style; so much do they study appearance, but in perfect innocence, not with any thoughts of love-making; but arranging their hair when they go to battle, to make themselves tall and terrible, they adorn themselves, so to speak, for the eyes of the foe.