Beautiful as a lawn shade tree, but perhaps more appreciated for producing a tasty crop of nuts, pecan trees (Carya illinoinensis) are native to the southeastern and central United States. Abundant sunshine and a well-drained soil are key for the pecan tree's growth and health. Its roots are deep-penetrating and are best transplanted only when very young saplings or as established trees already grown in containers. Pecan trees are grown in US Department of Agriculture hardiness zones 5 through 9.
Pecan tree roots warrant tender loving care, especially when first planted. Newly germinating seeds quickly grow a slender, deep taproot and falter if harmed during transplanting, according to the American Horticultural Society's "A-Z Encyclopedia of Garden Plants." The University of Florida comments that a mature pecan tree's roots potentially penetrate as much as 10 feet deep, and most of the feeder roots that absorb water and soil nutrients remain in the top 12 inches of topsoil.
Roots grow best in a moist, fertile soil rich in organic matter. Pecan trees grow in a wide array of soils, from sand and loam to clay--all must have good drainage. Special care is required to establish pecan trees, as their root system is so deep. Texas A&M University recommends choosing a location where you know the topsoil to be a depth of at least 3 feet; the University of Florida suggests 5 feet.
Pecan trees infrequently are available for purchase as container-grown plants. These are often larger-sized specimens that require considerable resources to move and plant. Horticulturists with Texas A&M University comment that most pecans are purchased and received as bare-root plants. If the roots on sapling pecan trees are broken, establishment is poor during the first growing season. Generally speaking, if the pecan fails to grow much the first year, it often is because of a damaged root system during planting or the bare roots drying out.
The best root growth after planting pecans results in a warm, moist soil. Texas A&M University lists several issues that can kill or greatly diminish growth of the young pecan tree after planting. They include: planting the roots too deeply, competition from aggressive grass groundcovers, soil that is too wet or too dry, or presence of synthetic fertilizers in the backfill soil around the roots. The University of Florida recommends pruning away one-third to no more than one-half of the height of the pecan tree to create a better shoot-to-root ratio, but never create a tree shorter than 4 to 5 feet in height.
Texas A&M horticulturists share the radial spread of growing pecan tree roots extend at least two times the width of the branch/leaf canopy. After initial planting, a weed-free area with a layer of organic mulch extended at least 6 feet in all directions around the trunk allows roots to grow their best.