For most of my fifty years in the nursery and garden center business the sale of a plant, shrub or tree meant the additional sale of peat moss and cow manure for they were the recommended soil additives when planting. It was the thirty dollar hole for the twenty dollar plant!
Research has shown that these additives discourage root growth beyond the improved soil area so current thinking recommends adding nothing to the soil at all. It is best to dig a whole deeper and two to three times larger than you need, back fill the hole and then plant. This will loosen the soil surrounding the root ball and make for better water retention when watering.
I have put away my trowel and use a shovel for quick and easy planting! New plantings should be watered two or three times a week. The entire area that was dug around the plant should be watered to encourage root growth to grow outward from the plant.