I cover my deck with sunsails each summer. According to what I read, they block about 90% of UV rays. Most of my plants seem to just love it. I would think heuchera would very much love that. I don't think petunias would though. They tend to like more sun. Sweet potato vine likes anything, sun or shade, so it will likely be fine.

I will give it a try. My awning maybe 90% also. That would be great! I want to raise the pot to see all the color thru my great window which looks over the Tahoe mountains. I think that would be pretty.