When first planted, it is good to use a standard fertilizer or root stimulator to invigorate the roots.  You may then continue to use the standard liquid fertilizer or use a granular fertilizer that will feed over a 3-4 month time period.  You want to cease Nitrogen fertilizing in mid-August to encourage hardening off of new growth.  Add a 2-4 inch layer of mulch to any new planting.  This will help the soil hold moisture and will decompose over time offering organic nutrients into the soil and the plant.  It is best to leave a little bowl around the base of the tree or shrub with the mulch.  This will allow water to gather there and feed directly down into the root system. 

Newly planted trees and shrubs require roughly one inch or more of water per week when mulched.  The best method is to scrape away a section of the mulch and test the moisture level of the root mass with the tip of your finger.  It is critical that they stay neither too wet nor too dry, but evenly moist and well drained.  If it is raining often, there is less need to water. If it is drought like, it is up to you to water.