Backfill With the Dirt You Took Out of the Hole
For years, experts recommended adding compost, peat moss or fertilizer to the planting hole. However, most now agree that you shouldn't backfill with anything other than the original soil from the planting hole (despite what the plant tag says). Soil amendments in the planting hole can discourage the tree roots from spreading into the surrounding soil and can cause poor water drainage. Also, in some instances, fertilizers can kill young roots.
Use a spade to backfill around the tree with the dirt you excavated when you dug the hole. Be sure to keep the tree properly in place (right depth, straight up and down) and shovel in the soil evenly around the roots as you backfill. Once the hole is about half filled in, run water around the roots to eliminate air pockets in the soil and continue filling with soil. The tree will move easily until the hole is completely filled.
Mulch Wide, But Not Deep
Mulch holds moisture, moderates soil temperatures, reduces competition from grass and weeds, and prevents lawn mowers and trimmers from nicking the trunk. Mulch also helps insulate the ground, keeping it cooler in the summer and warmer in the winter. Make a 3-ft. (or larger) circle of mulch 2 to 4 in. deep around the trunk. But don't mulch too deep. This can create surface drainage problems and deprive roots of oxygen. Keep the mulch 3 or 4 in. from the trunk to avoid disease, rot and pest problems. Mulch, like other organic matter, can have bacteria and fungus, which can spread to the tree and harm or even kill it. Some good mulch choices are shredded bark or composted wood chips. Don't use woven or plastic landscape fabric or other weed barriers underneath the mulch. These can cause major problems later on as seeds grow roots down through these materials and anchor themselves into the barriers.
Leave a Protection Zone
When you plant your tree, leave a circular area around its trunk for a small flower bed. The flowers are not just attractive; the bed also establishes a buffer zone so that lawn mowers and trimmers can't nick or cut the bark. (String trimmers are a young tree's worst enemy!) For added protection, install vinyl edging to keep grass out of the bed.