Does My Tree Need To Be Fertilized?

This Tree sure looks sick, but does it need to be fertilized?

Trees are amazing plants. And I often think that point is missed when people think about trees and their health; that trees are living, growing, compartmentalizing, highly complex plants. So in that context, we need to change our thinking when it comes to fertilization and plant health.

First, lets look at how much larger trees are than every other plant thats out there (I’m referring to biomass). Trees have so much more material (biomass) to deal with and organize than the common house or garden plant. Especially, when we try and fertilize or compare grass to trees! Unlike your garden tomatoes or a field of corn, trees do not use soil nutrients like they do. If trees were struggling for nutrients, how would they still get so big? The answer is they are not struggling for soil nutrients. Trees are very efficient at gathering nutrients and often have help from beneficial fungi, termed micorrhizae.

There are many types of nutrients in the soil and they are put into two groups; Micro-nutrients and Macro-nutrients. The micro-nutirents can become a limiting issue with trees, but fertilizing will not fix that problem. Because fertilizer is made up of macro-nutrients Nitrogen (N), Phosphorous (P), and Potassium (K). And here is where it gets interesting and why fertilization of trees is rarely necessary.

Trees, unlike other plants, only rarely and every so slightly use phosphorous and potassium. Therefore, its rarely ever limiting in the soil or a problem for the tree to absorb, so adding it to the soil to ‘help’ the tree is just a waste and it often runs off or helps the grass grow.

All thats left then, is nitrogen. Nitrogen is a great nutrient for helping the plant to push new growth. That is all that it does. Thats why we add it to our tomatoes and other plants so they grow and give us plenty of food or flowers. However, in trees, if they do that too much, they spend to much stored energy that is required to fight of pests, reproduce, compartmentalize wounds, grow roots, and the countless other processes that trees do in order survive. In other words, if you give a tree too much nitrogen, you can actually kill it. It may look great in the short run, but trees are not short term plants. They live for centuries! All of our other plants that we throw fertilizer at are short term plants. Garden plants only live for one season, and the grass in your lawn only lives for a short time.

The whole point here is that trees rarely, rarely ever require fertilizer.

The picture of the sick tree above is chlorotic. This is a micro-nutrient deficiency of either Iron (Fe) or Manganese (Mg). If fertilizer is applied to this tree, it would kill it. The ‘fix’ in this instance is to give the tree exactly what it needs in the micro-nutrient and then to use growth hormones to help the tree grow a stronger root system so it can absorb more of the nutrient on its own later. The cause of this particular problem is a soil pH problem and not a nutrient deficiency. Micro nutrients are rarely ever deficient in most soils.

This leads me to my last point. If your tree is sick or having problems. First have a soil test conducted to see what you have and then a decision can be made as to what the tree needs. Do not waste your time and money fertilizing a plant that doesn’t need it.