In this contribution, an overview over a numerical scheme for the crack modelling of spruce wood under tensile loading is given. A material model for biaxially stressed spruce wood with consideration of the effect of knots on the strength properties has been developed. A necessary feature of this material model is its ability to treat cracks by means of the so-called smeared crack concept. For this reason the consideration of a so-called characteristic length in the corresponding evolution laws of the strength values is required. The successful implementation in the material model is shown by means of various numerical examples.