Late in April I dug up a little crabapple root sucker and planted it in a pot with compost and (what I think is) good drainage. So far it is alive- some leaves yellowed when I didn't water it enough one day, but the leaves are mostly green and look okay. However, it hasn't put out any new growth. Is this normal or is there something I need to be doing to ensure the tree's survival?

Could you please provide a picture of the tree?

Thanks, Clicio. I have attached photos from two sides to this post.

It looks OK to me, why don't you wait a little?
On a side note, your soil doesn't look as draininga s it could be.