It depends on how much oil your hair retains!
Wash your hair every 2 to 4 days.
Most hair care professionals sing of the perfect morning hair routines and make presumptive blanket statements that fail to recognize the diversity of hair styles and types we encounter in the real world. A Caucasian who surfs regularly on the beaches of cape town and a Malay who works in a corporate office five days a week should have very different experiences when dealing with their hair.
This is why I always recommend a variety of options when asked for hair wash advice. If you're having trouble, here's a basic rule of thumb: Most coily and thick hair types require a lot more oil to remain healthy. If your someone with very thick or curly hair, I would recommend spacing out your washes in order to maintain as much natural oil as you can. If you sit on the other end of that spectrum, where your hair is straighter and thinner than others, you may be fine washing your hair every 2 to 3 days.
Of course to everyone reading this post, I have not seen your hair in person so it may take some trial and error but at the end of the day, you must invest the time into your hair and you will see the results. Guaranteed.