When using a crock pot, shouldn't I put things like celery and green
peppers in towards the last hour or two?

I never had a crock pot until I got one for my most recent birthday.
I've used it once thus far - to make vegetable soup - and followed the
directions in the booklet to the letter. The potatoes were fine, but
the frozen veggies were like mush! So, I'm thinking that perhaps
non-root veggies need a lot less time?