A tree with healthy roots typically yields a healthy above-ground trunk and leafy canopy. Providing a spacious soil that contains adequate moisture and nutrients allows for unimpeded root growth and faster, lusher growth of branches and leaves. Mulching the soil above the roots is beneficial, as it retains moisture, insulates the soil from extreme temperatures, reduces weed competition, and improves the soil's nutritional value and texture over time.
Tree roots serve many functions. They act to anchor the plant in the soil, they facilitate absorption of water and nutrients, and they store starches and sugars over the winter months that supply the energy for new leaf growth in spring.
Edward F. Gilman, professor of environmental horticulture with the University of Florida, attests that many trees may initially develop a carrot-like tap root when small, but as the tree grows, the root system becomes much more laterally branched. Occasional downward-growing roots from lateral branches aid in anchoring the tree, but roots continue to branch into smaller structures, eventually into fine, hair-like roots that actively absorb nutrient and water molecules.
Extent of Roots
Although the depth and structure of tree roots can vary among plant species, most tree roots grow in the top 24 inches of soil with smallest, most tender roots in the top 2-inches. Professor W.R. Jacobi of Colorado State University shares that even deeply anchoring roots typically penetrate no deeper than 3 to 7 feet. The root system extends anywhere from 2 to 4 times the spread of the tree's canopy, according to Gilman. For example, a tree with a leafy canopy that is 20 feet wide typically has roots that radiate outward to as far as 40 to 60 feet from the trunk, depending on the tree species, quality of the soil, and availability of moisture.
Tree Transplant Concerns
According to environmental horticulture professor Ed Gilman in "Your Florida Landscape," tree roots must be protected during planting activities to diminish harm and improve the establishment of the tree after transplant. Tips include shading roots from drying wind and sun during transport or the planting process as well as shading root balls to keep them cool. Plastic coverings may retain moisture but can allow heat build-up from ultraviolet rays during the day. Insuring the soil around the roots remains appropriately moist and cool once the tree is planted is a key component of increasing its survival and rapid establishment in the landscape.
Tree roots do not "seek out" water from pipes or other man-made hardscapes. Rather, they are opportunistic, growing more quickly or forcefully in soils that are conducive for overall plant growth. Compacted soils, those with hardened structures from heavy machinery weight or extremely dry clay can lead to tender small root death or prevent roots from moving into the soil structure. Extremely wet soils, depending on tree species, may also deter roots from moving into soil that is lacking oxygen or inhospitable. Rock hardpan (a layer of hard soil under a layer of soft topsoil), underground boulders and man-made hardscapes like asphalt or concrete roads, curbs, foundations and sidewalks can limit root growth depending on the depth of the material and the tree's typical root structure.