Should I fertilize established trees and shrubs?

FAQ
Question: 

Should I fertilize established trees and shrubs?

Answer: 

It is generally not necessary to fertilize healthy, vigorous trees and shrubs in the home landscape.  Most landscape soils in Iowa contain adequate levels of nutrients for trees and shrubs.  Plus, trees and shrubs that are growing in lawns that are fertilized on a regular basis are already being fertilized.  Poorly growing trees and shrubs may benefit from fertilization.  Poorly growing plants often exhibit sparse foliage, yellow-green leaves, or short annual twig growth. 

If necessary, spring and fall are the best times to fertilize trees and shrubs.  Fall applications should be made after leaf drop (mid-October through November).  Spring applications should be made in late March or early April before the trees and shrubs begin to leaf out.  Avoid summer fertilization as this promotes succulent, late season growth which may not have sufficient time to harden before winter.