Fertilizer - a double-edged sword often misused in an attempt to help sick trees
First: Stay away from stakes, spikes, liquids, soil injections, and trunk injections. Some of those methods of application are “snake oil” and others may work but cause long-lasting damage. Topical granular spreads are still the best bet for most situations.
Second: Most trees do not need fertilization. If there is a true nutrient deficiency present, that means something has gone wrong and applying fertilizer will only be half of the solution.
We often tell our 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 and are more than likely looking out for their profit not your tree.
- Our experience and that of many of our 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 trees unless a nutrient deficiency can be positively determined. And then and only then should the deficient nutrient be applied.
- The best method of applying nitrogen fertilizer in the proper amount is to add organic mulch directly over the soil under the canopy of the tree. The mulch, without a weed mat barrier, will gradually break down and release nitrogen at the rate trees require. See our mulching page for more info.
- 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. The level of nutrients actually 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.