T.F.
Well, we get trashed here in TX for our mum traditions which are crazy I know, but it is a part of the high school homecoming. I can think of things much worse, plus I'll do what my mom taught me and keep my mouth shut about other areas of the country and what they do for traditions which I find very awkward and silly as well.
They wear the mums on homecoming day, NOT to the dance. Can't let that mum mess up a good dress!! I was surprised at how large the garters and mums were, HUGE and I am glad this was not tradition when I was in school. We wore a single, live decorated mum... In MS.
As for the garter, don't do too much. My daughter's bf is a senior and his was a different color scheme. He is not a football player so she decorated it with things he liked..., etc. He decorated hers with cheer because she is a cheerleader and cute bf/gf trinkets. They only put first names on their mums.
They are going to daughter's homecoming in late Oct and she'll be getting another garter for him and she'll get another mum, just in her school colors.