Thank you for you question about landscaping around your tree. Edging can be done if you follow a few simple guidelines. Placement typically occurs at the "drip line" - the area where the moisture drips off of the tree. Because your tree is new you can decide how far out you would like to go. Attention to protecting the roots must be given when doing any digging. That is made easier because your tree is so young. When first planted Oaks establish a taproot, one large root that grows deep to reach the moisture. Following this roots branch out closer to the surface. You can use concrete or black plastic edging. With any edging you install the depth is important. You want to keep the soil level similar to what it currently is. Placement of additional depth of soil or mulch can affect how roots take in moisture and nutrients.