Stones

• Medium-sized stones provide an effective barrier from foot traffic and weeds. Flagstones and fieldstones are a few types you can use to add a rugged appeal to the yard. Use a spade to remove surrounding grass and create a trench for the stones. Edge in a circle to accentuate the tree's shape. Fill the space between the stones and trees with wood chip mulch to insulate the roots and prevent erosion.
  
  

Bricks and Pavers

• The uniform shape of bricks and pavers creates edging with a clean, polished look. Build a tree ring by setting bricks side-by-side for a wide border, or end-to-end for a narrow border. The resulting border adds sharp definition to trees. If your walkway, driveway or patio is paved with bricks or pavers, using them as borders helps to unify hardscapes with natural growth.
  
  

Wood

• If you have a wood fence, deck or handmade furniture, wood borders are a natural choice. There are two primary ways to use wood as a border. For a square or angled shape, use landscape timbers, or pressure-treated lengths of wood, for a simple, casual style. The other type of wood border consists of short wood posts that you hammer into the ground side-by-side. The result looks like an ornamental fence framing the tree. Cover the ground between the border and tree with mulch to accentuate the textures and different uses of wood.
  
  

River Rocks

• River rocks offer an informal alternative to structured borders. They come in a range of sizes, but are typically larger than gravel and smaller than paving stones. Smooth and rounded, river rocks contrast with the color and texture of trees and surrounding grass. Install a river rock border by removing the grass surrounding the tree and putting down landscape fabric to keep weeds from growing through. Rake river rocks evenly from the edge of the border around the tree. For a line of trees, create a single border around the bases for a clean, natural look.