Shade Tree Notes Blog

By Kelby Fite, PhD, Plant Physiology

After winter ends, your trees and shrubs will be working hard to establish spring growth. If your soil lacks nutrients (which most urban and suburban soils do), the overall health and appearance of those plants – their growth, color, and foliage – will suffer. In addition to provide proper nutrients to your plants, mulching provide many benefits for trees and shrubs. Properly applied mulch will moderate soil temperatures, reduce soil moisture loss, reduce soil compaction, provide nutrients, improve soil structure, foster beneficial microbial communities, and keep mowers and string trimmers away from the trunk. These benefits result in more root growth and healthier plants.

Plants are one of the few organisms that produce their own food. They do this by converting carbon dioxide and water into carbohydrates in the presence of sunlight through the photosynthetic process. In addition to water and carbon dioxide, there are 14 more essential elements required for photosynthesis, growth, defense, and reproduction. Each one of these nutrients is therefore critical in the physiology of the plant. Justus von Liebig’s “Law of the Minimum” states that the lack of any single nutrient can limit the growth and productivity of the plant when its concentration is insufficient, regardless of the abundance of other nutrients. The elements essential for plant health are divided into three categories: macronutrients, secondary and micronutrients (See Table 1). These categories are based upon the amount required within a plant. Often in landscapes, these nutrients are in low supply in the soil or are unavailable due to a high or low soil pH. A deficiency in one or more nutrients can have a severe impact on plant growth, aesthetics, and susceptibility to pests. Plants are efficient in their use of nutrients, and as such visual symptoms often do not appear until deficiencies are severe.


Figure 1: Mulch should be applied from the trunk to the dripline.

   Mulch Overview

 Figure 2: Mulch layer should be 2-4 inches thick and not be against the trunk.

    Mulch Thickness