They'll be fine, don't panic. Last year one of my pots of impatiens got so big it was attacking part of the driveway where my daughter was parking her car. She kept finding dead flowers on her car and was having a fit. One day while I was out she got the clippers and hacked the thing to almost nothing. then figuring I'd have a fit she moved the pot to where she thought I wouldn't find it. LOL as if I wouldn't find it in my walk around my gardens. anyway she beat me to the job and when I saw it I laughed about it. 3 weeks later it was filling the pot again and about 2 weeks after that it was on it's way to taking over a new spot, but not near anything else to get in its way

I love when Impatiens get to that point...they are so beautiful! They are the first flower I've ever planted outside, so I guess I've bonded with them--they encouraged me that I didn't have a brown thumb.
Hostas and Hydrangeas are pretty hardy so I don't think they'll be harmed by Impatiens "spreading their wings".

If you just pinch off pieces of the plant where they're interferring with the others's space, it shouldn't harm them. If you cut them rather than pinch, I think they'll still be okay. You just have to wait for them to hit that point of explosion again.

Also, when you pinch the stems, you can stick them right in the ground, water well, and they'll grow. Hardy little suckers. If there's any other space with part shade that you want to fill, you could do this.

Gee, I guess that answer my question about cutting my impatien bags to have them fill out again. They are quite leggy. Although it's late in the season I think I'll still give it a try. Last year I had the same problem and ended up trashing them in mid August because they looked so bad.

Dee
8>D

What are impatien bags?