Plant a green ash tree by choosing a site with full sun, digging a large hole and loosening the roots in the container before removing the tree. When choosing a planting site for the tree, sun exposure is more important than the type or pH of the soil. The tree can thrive in well-drained sandy soil, waterlogged clay or loam but doesn't grow well in partial or full shade.
Amend the planting site with compost to enrich the soil, and dig a hole that is as deep as and considerably wider than the plant's rootball. The denser the soil, the wider it needs to be so that the roots have space to grow and become established in the new environment. For instance, dig a hole six times bigger than the rootball in clay soil because it's harder for the roots to penetrate the soil.
Gently lay the potted green ash tree on its side, and roll the container over to help loosen the soil and roots. Gently pull the rootball out, and set it in the hole, spreading the roots out. Fill half the hole with soil, and water it well to settle the soil before filling in the rest of the hole. Tamp down the soil, and water the tree again. After 24 hours, spread a thick layer of mulch around the tree and water it again.