Where are you located and what kind of trees are they? That can make a huge difference :-) And you need to pull that mulch away from the base of the trees...at least a few inches.

I’m in Tennessee and the trees are Hickory. Thanks for the mulch info.

Geranium 'Biokovo' or 'Karmina' would look fine there.

Thank you!

Full sun plants probably aren't going to grow to their full potential there. I would stick with part-shade plants, which often can tolerate a pretty fair amount of morning/early afternoon sun. Stuff like hostas, ferns, Solomon's seal, anemone, etc etc -- there really is a wide range of possibilities. But -- I see the problem here being amount of moisture. I'm not familiar with hickory trees so I don't know how deep-rooted they area. If they root down and deep, you shouldn't have too much trouble; if they root out and shallow, though -- you are going to have a battle with dry soil. You can work around it, though -- it comes down to choosing plants that can tolerate dry soil and root competition and a pulling a couple of tricks of the magic bag while you're getting the plants established.

Thank you, mxk3!