Root Depth of Shrubs

Basic Growth Habits

• Shrubs depend on their roots to obtain water and nutrients, store water and nutrients, obtain oxygen and to anchor the plant to the ground. Roots grow outward two to three times as far as a shrubs branches, but the depth of the roots is not quite as predictable. As a very general rule, most shrubs roots are between 12 and 18 inches deep. At their deepest, a shrub's roots will go down 3 feet. It is always important when digging out a shrub to dig out as much of the root structure as possible.

Aeration

• Shrub roots generally remain in the first foot or two of soil because shrubs "breathe" through their roots and need, therefore, to grow in well-aerated soil. As a rule, soil is loser and has better air flow the closer to the surface it is. If the soil in which your shrub is planted is especially loose and well aerated, it is more likely that the shrub's roots will go deeper into the soil.

Moisture

• The saturation of soil is a large factor in the depth of a shrub's roots. If the soil is oversaturated, the plants root system will likely be shallow for a couple of reasons. First, it does not need to go any deeper to obtain water; also, oversaturation impedes aeration as air pockets are filled with water, and as a result, there is no oxygen for roots to take in at deeper levels. In excessively dry soil, roots will grow deeper in search of moisture in the subsoil. Though oversaturation is generally bad for shrub root systems, when a shrub is first planted, oversaturation is important, as it encourages initial root growth.

Nutrients

• The nutrients available in any given soil also affect root depth. On the one hand, shrubs in nutrient-deficient soil will expand their root system as deep as possible to find the nutrients they need to grow healthily. On the other hand, if soil nutrition is poor, root depth may be extremely shallow, as the shrub does not have the nutrients necessary to expand its root system in the first place.

Age

• Root structures logically grow deeper as shrubs grow older and larger, so the size and age of a shrub can be a good indicator of the shrub's depth. Usually, when a shrub is bought from a garden center, the root structure is 8 to 12 inches deep. Depending on the plant and all of the above-mentioned factors, the roots can be expected to grow 1 to 3 inches deeper a year, generally up to 18 inches.