We have a semi-circular planting area on the west side of our backyard that gets morning sun and afternoon shade. Planted from left to right are a butterfly (about 10 feet tall), a coral bark (about 12 feet tall) and an inabe shidare (about 5 feet tall). We had groundcover that my husband decided he didn't like and so now it's just bare dirt. Any suggestions on what to plant underneath the maples, if anything? We live in the southern SF Bay Area by Stanford University if that's helpful.

We also have some beach ball size stones that we can put there but I'm having trouble figuring out an arrangement for them. I thought I read somewhere that the stones should be placed naturally and in 3's or 5's? Any suggestions appreciated.

Thanks in advance.