It's notoriously difficult to get anything to grow under a maple tree. They have surface feeder roots that suck out all the available water and nutrients and anything you plant won't do as well there as elsewhere. That being said, since your tree is small, you might have a few years before this is a huge problem. (Larger trees are shady too, which further makes it hard for things to grow.)

There are certainly plenty of things that will grow under a maple, however. Many groundcovers, such as vinca, bishop's weed, and lamiastrum are quite fond of such conditions. A nice plant to try would be hosta. Pretty much anything that will tolerate dry shade will be worth a try.

Lillies need full sun so will not do well after the tree grows to shade them. You might have better luck with daffodils.

For now, I'd put up your rock border, then fill in the space with annuals each year. They will bloom all season. Then when your tree grows you can begin to switch over to shady/woodlandy sorts of things.

Do you know what kind of maple it is? A lot of them around here are fast-growing silver maples and the like, and they are a little hard to plant under once they're of decent size. Hostas are a good standby. And Epimedium can take it both shady and dry. Bulbs will probably do pretty well--our neigbors' yard used to have a spring carpet of deep blue scilla which was very pretty under the trees, and I used to grow tulips under our mature silver maple. Groundcovers might be your best choice overall. I wouldn't plant anything you're not willing to dig up and relocate (or happily give up on) at the first sign of competition-induced decline.

Also, since it's such a young tree, you might be doing it a favor if you don't plant much around it for a few years, so you don't disturb the root zone. This especially applies if it's a really nice ornamental maple.

Yeah maybe I'll plant in the flower bed and leave the little guy alone. I'm not sure what kind of maple tree it is, moved into the house over the summer. My backyard is where I would like to hang out over the summer. The yard is kinda small so I have to utilize the space wisely. The Maple was place sort of in the middle of the yard. I have quite a bit of evergreens on one side for privacy I guess, unfortunately they take up a lot of space and make my yard seem smaller. I kinda wish the evergreens were on the other side cause one of our neighbors is so nosy! He just loves talking to my husband and completely bypasses my hellos. One time he was snooping in our basement windows and always comes out when my husband is out. But if I'm out there he ignores me. At any rate, I want to garden and enjoy my backyard for the next 2-3 yrs since my husband wants to move out soon due to the neighbor. I would like lots of color and be able to enjoy some flowers. Went off subject here, but I will post pics next spring/summer when I get things together in my yard. Thanks for your help