Celery

This is the first time I've ever grown Celery.
I am getting some pale, sad looking stalks on the outside bottom of the plants. Is this normal? Not enough water? too much? Nitrogen?

I did a quick google and found Blanched plants lack green color, as the light source of celery is blocked out, which results in a paler color. 
So, I guess the lower leaves just are getting shaded from the tops.
Something learned.