A common misconception is that all trees need to be fertilized with high amounts of nitrogen and this will make them healthier.
While it is true nitrogen is the most common limiting factor of tree growth, it does not mean that more is better. By adding fertilizer, you seek to enhance some aspect of plant growth. For instance, gardeners add fertilizers to the garden to increase flowering or fruit production, and a high-nitrogen fertilizer will do that.
But is this what we want for trees?
Trees have an energy budget used for such functions as root growth, vegetative growth, flower production, photosynthesis, chemical defenses, physical defenses (including dense wood, bark and thick cell walls), hormone production and other components of tree life. The addition of nitrogen forces the tree to invest more of its budget in vegetative growth – sprouting, leaf production and shoot elongation.
When we encourage this additional vegetative growth, it is at the expense of other plant functions that maintain tree health. These plant functions are responsible for, among other things, producing hard, sound wood; warding off insects; resisting disease; and storing reserve energy.
High-nitrogen fertilizers promote rapid, weak, succulent vegetative growth that is prone to storm damage, insect attack and disease infestation.
Cell walls do not grow as thick, as large or as strong and contain fewer defense chemicals than normal cells. These cells produce weaker wood more likely to break in storms. Aphids have an easier time puncturing the cells to suck out valuable nutrients. These weak cells with fewer defense mechanisms also are able to ward off disease pathogens.
A fertilization program should not only provide a balance of proper nutrients for tree growth and development but should also help increase soil health.
A professionally applied fertilizer program should include such items as humic acids, beneficial bacteria and fungi, sugars and essential proteins. These items help improve the ecology of the soil.
Micro-organisms that live in soil provide natural aeration, organic matter decomposition, reduction of compaction, improved soil structure and increased fertility. Promoting these micro-organisms will improve the soil and thus improve your trees’ health and vigor. If you are using a professional company to fertilize your trees, ask what will be used. Make sure your company is using more than Coron, a trade name for liquid nitrogen.
One caution: If you are fertilizing your lawn, never use a weed-and-feed fertilizer. The herbicides in these products are made to kill broadleaf plants; most trees are broadleaf plants.
Robert Brudenell is a certified master arborist and owner of The Natural Way Inc. Send questions to robert@thenaturalwayinc.net.
