How big roots are on 15ft holly tree?

The root system of a 15-foot holly tree can vary depending on factors like soil type and moisture levels, but typically, the roots spread out widely, often extending 1.5 to 2 times the tree's height. The main roots may be several inches in diameter, while smaller feeder roots can be much finer. Generally, holly trees have a fibrous root system that helps them absorb water and nutrients efficiently.