Apply Mulch and Water
Apply a two- to three-inch layer of mulch around the base of the tree or shrub. The mulch will help the new plant retain moisture at its roots and suppress weeds from growing. It also creates a barrier around the plant so string trimmers and mowers won't damage the trunk flare and bark. Keep the plant evenly moist, but not too wet, throughout the growing season; water about once a week, adjusting accordingly to periods of drought and rain.
When watering a newly planted tree or shrub, make sure to water not only the root ball but also the undisturbed soil immediately surrounding it. This keeps the soil moist at the root level, making it more inviting for the roots to penetrate.