2.5 weeks w/out washing
At first, I went a few MONTHS without washing my hair. It was alright.. your scalp does get used to it. But after a while I sort of couldn't take it anymore, so I washed it with Dr. Bronners shampoo. And it felt soooo amazing to have a clean scalp! I now wash it every 10-ish days, and it's fine! I have very dry hair too, so it's perfectly fine! It's just up to personal preference. I know people who don't wash their hair at all... and the scalp gets used to it if you can stand it!