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Slope greening is a nature-based solution that brings multiple environmental and societal benefits to urban built environments. The selection of plant species for this purpose is often based on their landscape values. However, the potential engineering functions of vegetation, such as pull-out resistance to soil sliding, have generally been ignored. Previous studies have attempted to use different root morphological traits to empirically explain the variations in pull-out resistance Pul, but the underlying root–soil load transfer mechanisms have rarely been investigated. This study used a validated three-dimensional (3-D) embedded beam element model in a finite element platform to parametrically investigate the effects of various root morphological traits on the pull-out behaviour of 3-D root systems. Simulation results showed that root systems whose morphology and branching pattern could gain more interfacial shear resistance (oblique second-order laterals in contrast to the horizontal case) and mobilise more root internal stresses (deeper branching point between first- and second-order roots) had higher Pul values. The third-order sinkers were effective in mobilising their tensile strength to resist pull-out only when they were within a certain distance away from the first-order taproot. A new integrated morphological trait was proposed to implicitly capture the different aspects of root–soil interaction mechanisms, and it contributed to approximately 85% of the Pul variability. Our study suggests that among the root systems that have the same volumes, those with either (1) more branch roots (BRs) but shorter lengths or (2) less BR but longer lengths have greater pull-out resistance and are thus more effective to soil stabilisation. © 2023 Elsevier GmbH