Ok this is my first time growing mj and I have 5 plants growing about 3 inches tall in regular dirt placed in styrofoam cups, only 5 out of 10 succesfully sprouted

and I think its because of the natural dirt. I still have 10 seeds left and what I am asking is how much soil I should buy(pounds)/what brand works good/any stores recommended. I only looked at Fred Meyer but they didn't have the right ph level so I left. I don't know of any nurserys so big department store names would really help because I don't have a car and don't wanna ride on a bus all day.
Thanks