Softwoods have a repetitive variation in stiffness over their growth rings, which is due to the difference in cellular structure between the latewood and earlywood. In this paper, the influence of the repetitive stiffness variation on radially growing cracks is studied by detailed finite element analyses, in which the wood material is represented by a layered orthotropic continuum. The distribution of stress around the crack is found to be very different from crack tip stress fields in homogenous isotropic materials. The latewood layer ahead of the crack experiences a significant tensile stress, which indicates that formation of new secondary cracks ahead of the primary crack front is a likely mechanism for crack propagation. This mechanism is also favoured by the fact that the primary crack is subjected to a significant shielding from the stiff latewood, which tends to arrest the primary crack in the soft earlywood layer. Analyses are performed for materials with various growth ring widths, and the calculated results are compared with reported experimental observations.