Numerical modeling of interacting flow processes between roots and the soil is essential for understanding the influence of different root geometries and types on the hydrosystem. The coupling of two software tools enables the analysis of water uptake of plant communities, one modeling the water flow along a network of resistances from the bulk soil along radial soil disks toward the root system up to the root collar, while the second tool is covering the nonlinear dynamics of water flow within soil by a three-dimensional Richards model. Appropriate methods for geometric coupling, fast coupled parameter exchange, and coordinated parallelization have been developed to ensure an efficient functionality. An adaptive time stepping with automatic control guarantees the stability of the solution of nonlinear problems.