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Plant Health Care, Part 2- Roots and Soils

© Wesley Ford

"Plant Health Care" has been the buzzword in the arbor industry since the early 90's and seeks to look at trees from a holistic point of view. Like humans , plants are subject to environmental stresses that affect growth and vigor and ultimately longevity and soundness in the landscape. Utilizing a "Plant Health Care" approach involves looking at the functioning of all plant organs and the environment in which the plant lives.

Since the root system is the basis for support and water and nutrient uptake, much emphasis is placed on evaluating the health of the root system and the condition of the media in which it grows, the soil. Roots are not just strands of tissue that creep out into the soil and just suck up water, nor is the soil just dirt that provides a convenient place for plant roots to grow. Soil is an ecosystem consisting of non-living mineral and organic particles and living organisms, including fungi, bacteria, other microscopics, plant roots, nematodes, insects, mammals, worms and other micro-biological and animal forms of life. Managing the physical properties of soil (particle size, organic content, pH, nutrient content) is science. Managing the living component is an art. In plant health care, we seek to understand how the former impacts the latter and act accordingly to benefit the landscape we are focusing on.

Roots are the plant organs responsible for the uptake of water and ingestion of many nutrients. Fine, nearly microscopic root hairs are in contact with the soil and slurp up available moisture and absorb nutrients that are nothing more than chemical compounds existing in the soil solution and on the surface of soil particles. Roots also provide support for the plant, anchoring it in place. For trees this function is integral to the structural integrity of the tree. A third major function of root systems is energy storage. Simple sugars produced in the leaves are converted to starches for long-term storage in roots. This is the source of energy for growth following dormancy.

Tree roots also respire, which is a gaseous exchange of carbon dioxide for oxygen. Tree roots are consumers of energy and burn sugars produced in the crown and thus utilizing oxygen. Like in animal respiration, CO2 is released. Thus tree roots need access to atmospheric oxygen in the soil space. Since air penetration into the soil is limited, the vast majority of the root system, over 80%, exists in the top 12 to 18 inches of the soil. This is the living portion of the soil, where all the biomass exists. Some "tap" roots penetrate as deep as the soil profile will allow and serve as anchors and provide access to deep moisture. Little nutrient or gaseous exchange occurs through tap roots. These roots penetrate mineral sub-soils. Rooting depths of tap roots can be restricted by physical boundaries such as hard pans, very rocky layers, bed rock, and high water tables. Rooting depth can also be limited by chemical barriers such as lethal levels of chemical compounds.