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PREVENTING GIRDLING ROOTS How a Healthy Root System Serves as the Heart and Backbone for a Well-Established Plant By Amy Dismukes, Tennessee State University Extension Area Specialist
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rowers and landscapers are existentially aware of plant roots, but many may not fully appreciate the importance of these vital resources. Plant root functions are comparable to the services provided by our own arteries and veins. The consequences of root rot and vessel blockage are just as significant to plants as they are to each of us. Roots absorb and transfer moisture and minerals throughout the plant, as well as provide support for the above ground portion of the plant or tree, hence their comparable role as heart and backbone. There is a fine balance between the root system and the top of the tree; if part of the root system dies, a part of the crown may also die (Perry 1982). If roots are not present or cannot function as intended, the tree will eventually die.
Not All Roots are Created Equal There are two general categories of tree roots, woody structural roots and non-woody feeder roots. The health and well-being of both are imperative for maintaining a healthy canopy and plant. In fact, unimpeded root function is as important to photosynthesis and plant performance as is health of the leaves (Perry 1982). Woody structural roots are large lateral roots that form near the root collar at the base of the trunk, contribute to the structural support framework, and help anchor the tree. The abundance and arrangement of these roots will be different for each tree species (Perry 1982). Woody structural roots also serve as a carbohydrate sink and provide a location to store the carbohydrates generated from photosynthesis for future use by the tree.
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Woody roots generally can be found 8 to 12 inches below the soil surface and these roots can extend well past the drip line of the tree. In mature landscape trees, woody roots may become visible above the soil line. In trees that form taproots, which are thick, long roots that penetrate straight down into the ground, the taproot may be among the longest woody roots. For oaks growing in optimal soil conditions, the taproot may extend nearly as deep as the tree is tall. Not all tree species form a taproot, which may make these species less stable in heavy winds, light soils, or if a root rot fungus becomes established. Non-woody roots, also known as feeder roots, are fibrous to hairlike roots that extend away from the sides of larger, woody roots. Feeder roots penetrate into and spread mostly through the upper soil surface and may emerge into decomposing leaf litter, or humus, when this organic layer is present. Feeder roots make up the largest surface area of the tree root system. These fine roots are critical for tree growth and development. Fine roots connect to the leaves through an elaborate plumbing system that extends across larger transport roots, trunk(s), branches and twigs. Nonwoody roots are much smaller in diameter than woody structural roots, yet they perform critical functions for the tree. Feeder roots absorb water and nutrients from the soil and then transport those resources to the tree; similar to the way that your heart pumps oxygen, nutrients, and blood, feeding your body. Most trees also have root hairs that extend away from the feeder roots, further increasing the root surface area and vastly enhancing the nutrient and water uptake capability of the tree. If the soil conditions are healthy, the surface area covered by feeder roots can grow far beyond the drip line, often extending out as far as the tree is tall.
