I wash my hair once a week (whether it needs it or not :-D)--but we curly-haired types tend to have dry scalps.

I went shampoo-free for the winter several years ago; my hair/scalp never smelled or felt greasy, but my hair looked...flat. These days, I've switched to -cone-free shampoo, and am contemplating switching from shampoo to conditioner.

Haven't tried the baking soda/cider vinegar regimen, but I've used dry oatmeal as a scrub. Even scalp massage with a fluffy towel helps absorb excess scalp oil.