Ask Mr. Smarty Plants

From the Native Plant Database on our website: Eastern red cedars (Juniperus virginiana) are evergreen, aromatic tree with trunk often angled and buttressed at base and narrow, compact, columnar crown; sometimes becoming broad and irregular. Pyramidal when young, Eastern red-cedar mature form is quite variable. This evergreen usually grows 30-40 ft. but can reach 90 ft. Fragrant, scale-like foliage can be coarse or fine-cut, and varies in color from gray-green to blue-green to light- or dark-green. All colors tend to brown in winter. Pale blue fruits occur on female plants. Soft, silvery bark covers the single trunk.

The most widely distributed eastern conifer, native in 37 states, Eastern red cedar is resistant to extremes of drought, heat, and cold. Red Cedar can be injurious to apple orchards because it is an alternate host for cedar-apple rust, a fungal disease. First observed at Roanoke Island, Virginia, in 1564, it was prized by the colonists for building furniture, rail fences, and log cabins.

Nan Hampton, answered a similar Mr. Smarty Plants question previously and wrote:

The US Forest Service database says:  "Eastern red cedar generally has a shallow, fibrous root system, though roots of mature Eastern red cedar trees may penetrate 25 feet (7.6 m) and lateral roots may reach 20 feet (6 m).  Eastern red cedar seedlings have penetrating taproots and may later develop a lateral taproot system.  The deep, early taproot is usually replaced by an extensive, shallow root system with age.  Even 1st year seedlings begin developing a long fibrous root system, often at the expense of top growth.  The root system may be deep where soil permits, but on shallow and rocky soils eastern redcedar roots are very fibrous and tend to spread widely.  The development of a lateral taproot with age may also enable eastern redcedar to persist on outcrops and shallow soils."

The US Forest Service Silvics Manual says that the soil condition determines whether the tree develops a deep tap root or spreading lateral roots.  In thin rocky soil fibrous lateral roots will be predominant; but, if the soil permits, the root system may be a deep penetrating tap root.  So, if your soil is good, you shouldn't have great concern about lateral roots.