My growth rate tripled when I started washing more frequently. I know it wasn't the result of anything else because the frequency was the only thing I changed.
Washing frequently is actually more likely to cause your scalp to produce more oil, as it keeps trying harder to replace what you wash away. However, you have to find a balance because although your scalp can keep itself from drying out, your hair can't. If your hair is highly textured or particularly long, the oil from your scalp may not travel all the way to the ends. Of course there are other things that may dry your scalp like bad ingredients in your products, minerals in your water, or you might just have drier skin. I believe the fact that my hair isn't drying out even though I live in a hard water area is due to increased scalp oil production, using high quality conditioners that don't just COAT the hair, and using mild shampoos. Also, doing scalp massages can help distribute the oils better in your hair.