Should I mention my blog in my SOP?
Yes.  You could mention it in your SOP and/or in your CV.

I have received some applications from students in which they mentioned a technical blog, and so far it has always left a positive impression.  In my opinion, keeping such a blog demonstrates:


Maturity in writing and communicating (especially if your blog communicates something technical in an informal way that is not sloppy).
Organization of thought and effort.
Initiative.
Love for learning ideas relevant to your discipline.