Thanks for your question regarding arborvitae root system.

 The root systems of arborvitae are generally shallow depending on the variety and they may spread to the drip line edges of the branches. The major root depth of a large arborvitae variety can reach 18-24 inches deep, while roots of a smaller variety such as Emerald Green, reach 8 inches deep. Emerald Green is popular locally, it has a pyramidal form growing to a height of 10-15 feet by 5 feet wide, making it much smaller than the species.

Mr. Bowling Ball Eastern arborvitae (Thuja occidentalis ‘Bobazam’) is a small, compact, rounded shrub, growing just 2 to 3 feet high and wide. Dense, fine, soft, scale-like, gray-green foliage. Useful in foundation plantings or rock gardens, as an accent plant or in containers, though container must be insulated to protect roots in winter.

Here is some other information on Mr. Bowling Ball Arborvitae - Thuja occidentalis 'Bobazam'

Height: 30 inches

Spread: 30 inches

Sunlight:  Full Sun to Partial Shade

Hardiness Zone: 4

Other Names: American Arborvitae, Eastern White Cedar

Description: This tiny shrub just demands to be loved by all gardeners, with very unusual threadlike sage-green foliage and an extremely dwarf, compact form that requires no pruning to maintain its perfectly rounded shape; ideal for rock gardens and detail use

Ornamental Features:

Mr. Bowling Ball Arborvitae has attractive grayish-green foliage. The threadlike leaves are ornamentally significant but remain grayish green through the winter. Neither the flowers nor the fruit are ornamentally significant.

Landscape Attributes:

Mr. Bowling Ball Arborvitae is a dense multi-stemmed evergreen shrub with a more or less rounded form. It lends an extremely fine and delicate texture to the landscape composition which should be used to full effect.

This is a relatively low maintenance shrub. When pruning is necessary, it is recommended to only trim back the new growth of the current season, other than to remove any dieback. It has no significant negative characteristics.

Mr. Bowling Ball Arborvitae is recommended for the following landscape applications;

• Mass Planting
• Rock/Alpine Gardens
• General Garden Use
• Container Planting

Plant Characteristics:

Mr. Bowling Ball Arborvitae will grow to be about 30 inches tall at maturity, with a spread of 30 inches. It tends to fill out right to the ground and therefore doesn't necessarily require facer plants in front. It grows at a slow rate, and under ideal conditions can be expected to live for approximately 30 years.

This shrub does best in full sun to partial shade. It prefers to grow in average to moist conditions, and shouldn't be allowed to dry out. It is not particular as to soil type or pH. It is somewhat tolerant of urban pollution and will benefit from being planted in a relatively sheltered location. Consider applying a thick mulch around the root zone in winter to protect it in exposed locations or colder zones.

Mr. Bowling Ball Arborvitae makes a fine choice for the outdoor landscape, but it is also well-suited for use in outdoor pots and containers. It can be used either as 'filler' or as a 'thriller' in the 'spiller-thriller-filler' container combination, depending on the height and form of the other plants used in the container planting. Note that when grown in a container, it may not perform exactly as indicated on the tag - this is to be expected. Also note that when growing plants in outdoor containers and baskets, they may require more frequent waterings than they would in the yard or garden

Problems: This arborvitae is pest and disease resistant. Fungal leaf blight may occur, causing spotted foliage. The only occasional pests might be leaf miners, spider mites, scale, and bagworms. Use horticultural oils and manual methods to combat. Deer could be a problem too.