How often should a very thick & long ,thigh-length Hair (normal),be washed ?

For normal hair, twice a week at the most unless you do something like go mudding or swimming. That is is you are trying to keep the hair healthy or grow longer. The more it's washed the more you strip it of its vitamins, what little it has left. Besides, unless you're going to gym like in high school your hair really doesn't get that dirty.

Edit: My hair is about 3 inches from my waist.

How often should a very thick %26amp; long ,thigh-length Hair (normal),be washed ?

I have long, very thick hair...four inches below my shoulders.

I take a shower everyday; however, I wash it once every other day to retain the natural oils in...making sure it doesn't dry.