By Jeff Wilson, Certified Arborist #IL0099A
Trees require nutrients to live and thrive. When one or more of these nutrients are deficient in the soil, the tree will not reach its full landscape potential, will be more susceptible to disease and insect problems, and will have a shorter life than a similar, well-fertilized tree. Trees in urban and suburban environments are often under high stress conditions due to low moisture availability, soil compaction, physical damage, nearby construction, and competition from turf and nearby trees and shrubs.
Remember, trees are continually removing mineral elements from the soil. In a native forest, elements are recycled as leaves drop down to the forest floor and decompose. In most landscapes we interrupt this process by raking and removing leaves in the fall. Without periodic fertilization mineral elements will become deficient.
The objective of the fertilization is to put the nutrients where they will be best taken up by the trees roots. In practice we focus our fertilizer under the canopy, as that is where the greatest concentration of roots are.
The fertilizer must also be placed underneath the roots of competing plants such as grass or other ground cover. Spreading fertilizer on the lawn may make your grass greener, but it will likely not help your trees.
Why Fall is a Great Time to Fertilize!
One of the most important steps for proper tree care is the application of the correct fertilizer before the weather takes a cold turn. This is essential because trees need to have enough nutrients to help them remain healthy during the winter and to be able to have a jumpstart in the spring when the weather begins to warm again.
When we see the above ground portions of trees going dormant by leaves changing color and falling we may think the whole tree is going dormant but this is hardly the case. In the ground the roots are active and growing whenever the ground is not frozen and will continue to grow through much of the Winter.
Why Talk About Fall Fertilization Now?
Yes, it may seem odd to you that we use this space in our Summer newsletter to speak to you about Fall fertilization. The reason we do, is that now is a great time for your Arborist to check on the health of your trees to see if they may need to be fertilized. The color of the leaf can be an indicator of a problem that can be helped with the application of a specific fertilizer during the Fall season. We don’t use the same formulation for all trees, your Arborist will suggest the best for your trees specific need. In fact, one of the applications we often prescribe for trees that are very yellow in appearance can only be applied in the Fall.