It "could" be too wet for them- they need less water than regular impatiens from my experience, but not allowed to dry out either in high temps. I've not heard of root pruning, and I'd probably try taking cuttings and start rooting those instead, although propagating NG's are not as easy as regular impatiens for me, but might be worth a try.
-Nan

Yes it was too wet, the roots where mush. I tossed it out and replanted the basket with regular impatiens. I have a whole bed of N G's so did not need to have any more.

indy- sounds like a plan to me! I'm highly in favor of the toss and replace method myself. LOL
-Nan