Fertilizer and Trees

Fertilizer – a double-edged sword often misused in an attempt to help sick trees


I often tell my customers the quickest way to know if a tree service really knows about trees and tree health is to see how they propose to help a sick tree. If they try to sell you a fertilizer program, then they very likely don’t know what they are doing. Then they are looking out for their profit not your tree.

  • My experience and that of many of my more knowledgeable colleagues is that a sick tree has a root problem not a nutrient deficiency.
  • The most visibly effective part of most fertilizer programs is the nitrogen in the fertilizer. But most of the research indicate that top growth not root growth is stimulated by nitrogen fertilization. Think about it…
    • If nitrogen stimulates more top (leaf) growth, won’t the extra leaves put additional stress on an already stressed root system by requiring more water?
    • Nitrogen fertilizer is not recommended for sick or declining unless a nutrient deficiency can be positively determined. And then and only then should the deficient nutrient be applied. For more on nitrogen fertilization, go to Dr. Ed Gilman’s web site.
  • The best method of applying nitrogen fertilizer is the proper amount is to add organic mulch directly over the soil under the canopy of the tree. The mulch, without a weed mat type barrier, will gradually break down and release nitrogen at the rate trees require. See the mulching page in this web site.
  • A soil test may indicate what nutrients are in the soil but will not tell you what nutrients have actually been taken up by the tree. That level of nutrients in the tree is an important bit of information. The only method to determine the actual nutrient level in the tree is to obtain a leaf tissue sample and send it to a laboratory set up to perform such a tissue test. Most land grant universities that operate the Extension Service have a laboratory in the soils department that is equipped to perform a leaf tissue analysis. The University of Florida Soils Laboratory can be reached by clicking the soils lab name above.

Palm Fertilizer

Palm trees, especially the exotic (non-native) palms, have different fertilizer requirements. For more information on palm nutrition, go to the palm section of this website.