We don't recommend fertilizing trees unless a soil test shows the need.  Please read this publication and consider the things listed below before doing so

• http://www.ext.colostate.edu/ptlk/1708.html
• Never fertilize newly planted trees, only established trees
• Evergreen trees require even less fertilization than deciduous trees- test your soil every 5 years to determine need
• Never fertilize insect or disease infested or stressed trees
• Never fertilize after new leaves have emerged in spring or before hardening in fall
• Use the lowest rate of recommended Nitrogen and never put in the back fill or leaves may burn
• All fertilizers are salts so a slow release fertilizer would be best
  
• Fertilizing results in top growth at the expense of root growth
• fertilizing prohibits plants from taking up water so watering would need to be done with extra care