You may think we are dragging this topic out to its limits; but bear with us. This process is really important to the health of your new shrub.
Positioning the Shrub in the Hole
Lift the shrub by its rootball, not by its stems, and set it into the planting hole. Position it so it is vertical and oriented best side facing front. Verify, one last time, that it is set at the proper height. Place a shovel handle or a yardstick across the open hole after setting the shrub in it to determine if the crown or soil line on the stems is level with, or better yet, slightly above, the level of the surrounding ground.
Reach down into the sides of the hole and cut away all twine and burlap that you can reach if the rootball is wrapped. Cut off the top sections of a wire basket if it is present. Position roots that protrude from the soilball outward toward the sloping sides of the hole, prior to filling it with soil.
Filling the Hole
Since the goal is to encourage shrub roots to grow beyond the planting hole as quickly as possible, do not add fertilizer or enriched soil to backfill the hole. If the soil in the hole is too rich, young roots will be inclined to stay in it and not spread widely.
Backfilling with just the soil which you dug out of the hole will acclimate the shrub to its new environment and encourage it to seek out nutrients and moisture beyond the hole. If your soil is very heavy clay improve the surrounding soil with organic matter such as peat moss or chopped leaves or plant in a raised bed filled with loosened, improved soil. Never put sod, large rocks or construction debris into the hole as these materials will interfere with root development.
Forming a Water Basin
Shovel the soil into the hole around the shrub’s rootball, periodically tamping or firming it with your foot. Do not stomp so hard that you might break roots off down in the soil. Then add more soil until the hole is full. Form a waterholding basin out a bit beyond the edges of the original planting hole by mounding a ridge of soil about 3 inches high to act as a dike to prevent run-off. Then water thoroughly, filling the basin repeatedly until it no longer soaks in, to assure good soil to root contact.
Finally, cover the basin area and its rim with two to four inches of an organic mulch such as chopped leaves, shredded bark or wood chips. Do not pile it up against the shrub stems. Mulch conserves moisture, discourages weeds and keeps lawnmowers and string trimmers at bay. In the winter it buffers extreme soil temperatures.