Hi, Well I would first suggest that you surround the base of the tree with mulch such as shredded bark. This will help preserve soil moisture. As far as compatible flowers go, it depends on how much light the area gets. At this point, with a small tree, there's probably not much shade, but over time that tree will shade what's underneath it. So, for the first few years, perhaps you'd want to use some low-growing sun-loving annual flowers and over time, gradually begin planting shade loving perennials such as hostas underneath the tree. You can get more planting ideas by going to our Plant Encyclopedia on this stie and doing an Advanced Search.