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Tree Leaves with Chlorosis

Trees and shrubs are valuable elements in both public and private landscapes, and the wise investment of time and careful selection will only increase their value. Though there are several non-native species that do well in our fertile Illinois soils, we encourage the use of native species to promote disease resistance, suitability to native soils, and mitigating the spread of invasive species (even unknowingly).

Factors to take into consideration when choosing a tree species

  • light requirements
  • moisture requirements
  • soil pH
  • soil drainage

Using the right plant for the right site will factor into the overall health and longevity of a tree or shrub. It can take many years for symptoms of stress to appear, and by then it may be too late (or too large!) to move the tree to a more suitable site.

Determining necessity and time for fertilization

Though fertilization can help maintain tree vitality, I would first recommend establishing a need and purpose for it. If a soil test is not performed every 3-5 years, then nutrient concentrations may not be known. If we don’t know it’s needed, why waste product and time applying it? In most landscapes, healthy trees and shrubs do not require fertilizers, especially once they reach their mature size or if they are native species.

It is not recommended to fertilize a tree at planting time, as the tree’s energy is directed toward root growth and establishment and nitrogen applications can hinder root growth. If the lawn is already regularly fertilized, there is likely no reason to fertilize trees separately. Additionally, trees and shrubs should not be fertilized during drought conditions. Excessive fertilization can cause permanent damage to trees as well as affect water quality.

If you have completed a soil test, established a need for fertilizer due to a nutrient deficiency or pH issue, and have ensured adequate moisture to tree roots, you can find more information on tree fertilization methods in this great publication from University of Missouri Extension. The best time to fertilize trees, when necessary, is early spring or late fall after leaf drop.