When making a planter to wrap around trees, great care must be taken so that you don't kill your tree. Many people do not realize that a tree does not look the same below the ground as it does above the ground. Instead of the roots extending deeply into the ground, they spread out along the surface so that they can take in nutrients and water found there. By constructing a planter that girdles the tree trunk, you are mimicking conditions in which the tree is buried too deeply. The solution is to build a planter that does not smother the roots or rot the trunk.
Put on protective gear before beginning this project.
Mix up a hypertufa mixture using Portland cement, peat moss, perlite and sand in equal parts. Add water and mix to the consistency of a mud pie. Hypertufa is a cement mixture that dries to look like sandstone. It is frequently used in alpine gardens.
Form 24 half-spheres with the hypertufa mixture. Each half-sphere should be 2 inches thick. These will form the feet of your planter when dry.
Place the planter feet on a piece of plastic sheeting and double the plastic over to cover the feet. Allow to dry before continuing the project.
Cut the ends off of the Styrofoam containers and cover the outside with the hypertufa mixture. Attach dry feet to the mixture by pressing the flat side of the half-spheres into the wet hypertufa. Cover with plastic sheeting and allow to dry. Then flip over the containers and coat the inside with hypertufa.
Arrange your containers around the perimeter of your tree to form six sides. The feet will hold the planters above the ground and allow the roots to breathe. Connect the open ends of the containers to one another using chicken wire.
Coat both sides of the chicken wire with the hypertufa mix. Cover with plastic sheeting and allow to dry. Add as many coatings as needed to make the connecting sections as thick and solid as the sections reinforced with Styrofoam.
Fill the planter with potting soil and add your favorite flowers to the container.