You can give them a single application of fertilizer (such as 15-30-15 or 20-20-20) if you want them to fill out more. However, use it 1/2 strength. This way you can fertilize them monthly for best result.

I prefer to fertilize our impatiens. We have done trials with no fertilizer and they flowered poorly.

Also in your zone, they should have a fair amount of shade.

KDjoergensen,

Thanks so much for the reply, I just came in from applying a balanced fertilizer. Hoping to see lots of blooms soon.