Root Zones

• Almost all trees have a root zone that extends to the edge of the tree canopy. Many have root systems that extend even farther than the canopy. Estimating the root zone of your tree is a tricky business, and any weed and feed product applied over the root zone can harm or kill your tree.
  
  

Runoff and Leeching

• Even if you apply weed and feed outside the root zone of your tree, watering or rain can carry the pesticide into the root zone. Make sure the areas you intend to use weed and feed aren't uphill from tree root zones, and don't flood the lawn right after using weed and feed, because this will carry the herbicide away from the application zone.
  
  

Considerations

• Many extension services recommend not using weed and feed at all, and weed and feed products are even banned in Canada.If you instead fertilize your lawn when it needs fertilizer, and use pre-emergent herbicides safe to use in the root zone of trees if weeds become a problem, you are 100 percent sure not to damage your trees from weed and feed.