A realistic computer graphics (CG) model of root growth that accounts for the effects of soil obstruction and moisture variations is proposed. While the exposed parts of plants have been modeled extensively in CG, realistic root models have received little attention, and the potential effects of root characteristics on the growth of foliage has yet to be considered in detail. The proposed model represents roots as series of bend points and link points and defines the root systems as a layered structure formed by roots connected via link points. This approach allows for two general types of root systems based on branching probabilities of lateral and adventitious roots: main root systems consisting of a thick main root and thinner lateral roots, and fibrous root systems consisting of adventitious roots of relatively uniform diameter. The model also expresses the behavior of root growth in terms of hydrotropism, gravitropism, flexion and growth inhibition by assigning gravity, moisture and consistency parameters to underground voxels. The model is shown through simulations of various growth conditions to generate individualized root systems that reflect the growth environment and characteristics of the plant.