from
http://www.cmg.colostate.edu/gardennotes/132.htmlThe depth and spread of roots are dependent on the inherent growth characteristics of the plant and the soil’s texture and structure. Roots require adequate levels of soil oxygen, so growth habit will be a factor of the soil’s large pore space where oxygen is available. On compacted and clayey soils, roots will be shallow, remaining near the surface where oxygen is available. On droughty soils, the root system will spread farther, mining a larger soil area for moisture and minerals.
Figure 5. The typical rooting pattern of a tree is shallow and spreading
It is difficult to predict root spread of any plant. Under favorable growing conditions, the typical root spread of a tree includes:
90-95% in top 36 inches
50% in top 12 inches
Spreads 2-3 times tree’s height or canopy (drip-line) spread
On compacted clayey soils, the typical root spread of trees includes:
90-95% in top 12 inches or less
50% in top 4 inches
Potentially spreads five plus times the tree’s height or canopy (drip-line) spread
For additional information on the root system of trees, refer to CMG GardenNotes #103, Diagnosing Root and Soil Disorders on Landscape Trees.
Some plants are genetically programmed to have very deep, spreading root systems (i.e., they are more tolerant of low soil oxygen levels). This growth habit is an environmental adaptation. Examples include bindweed and prairie grasses.
Soil type is a key factor in water penetration and root uptake. Where soil allows, the primary water extraction depth extends to:
Flowers 18-24”
Turf 24”
Vegetables 24”
Shade trees 24-60”