If you are planning on planting a tree in soil that is sandy or with large amounts of clay, you will want to make sure that you mix in lots of compost. This ensures that your trees will have the nutrients that they need in order to grow large and healthy. Make sure you dig in good amounts of compost around the tree, so as it grows it will continue to reach nutrients. If you are planting in a new subdivision, you will want to make sure there is enough topsoil. Often construction in these areas removes most of the topsoil and not much is replaced.