Lawn fertilizer helps homeowners get the thick, lush grass they covet. Watch any lawn fertilizer television commercial, and it’s enough to get you off the couch and to the home improvement store in minutes. One easy application and my lawn will be the best on the street? Sign me up! Hold on one second — you have to read the fine print. Lawn fertilizer that includes weed killer is often dangerous for your trees. Applying it to the lawn above a tree’s root system could serio