Depth of Shrub Roots

Diversity

• Shrubs clearly adapt to the soil, climate and water conditions available to them. North Carolina azaleas, which generally reach heights of 4 or more feet, are shallow-rooted. Deep watering is defined as wetting the top 6 to 8 inches of soil. Photographs of the exposed roots of Arizona chaparrel evergreen shrubs display root systems twice to three times the depth and width of the visible shrub.

Shallow-Rooted Shrubs

• Some shrubs have fairly small root balls. Washington State's Department of Ecology lists ninebark, red currant and Nootka rose as having shallow roots that do not extend far from the plant. Arizona desert shrubs may have shallow root systems that extend twice the diameter of a shrub's canopy. Occasionally, a desert shrub will have both shallow roots and a deep root system, like the mesquite. Some shallow-rooted shrubs spread by means of underground rhizomes, making them good soil holders in areas threatened with erosion. Salmonberry (Rubus spectabilis), snowberry (Symphoricarpos albus) and Douglas' spiraeam (Spiraea douglasii) are only a few of the runner-spreading shrubs recommended for erosion control in the Pacific Northwest.

Deep-Rooted Shrubs

• Deep-rooted shrubs also contribute to erosion control, along with hedging and shading sunny yards. Red osier dogwood (Cornus stolonifera) and cascara (Rhamnus purshiana) are known for deep roots, as is oceanspray (Holidiscus discolor). Gardeners also find that in general native shrubs may have deeper and more tenacious roots than non-natives.

Transplant Concerns

• Nurserymen and other plant professionals caution that successful shrub growth depends on including an adequate root system when transplanting. Cutting major roots can result in long-term damage to shrubs and stunt growth. A general guideline is that the diameter of a transplant root ball should be roughly two thirds the diameter of the plant's branch-spread.

Factors Influencing Root Depth

• Soil drainage and water supply are two strong influences on the depth of roots for all shrubs. Heavy clay or rocky soil can impede root growth. Light or surface watering can make it hard for shrubs to establish deep and sustaining roots. Taking time to prepare soil and water deeply will produce shrubs with strong, healthy root systems.