In order to investigate the possibility of modelling plant motion at the landscape scale, an equation for crop plant motion, forced by the instantaneous wind flow, is introduced in a large-eddy simulation (LES) airflow model that was previously validated over homogeneous and heterogeneous canopies. The canopy is simply represented as a poroelastic continuum medium, which is similar in its discrete form to an infinite row of identical rigid stems. Only one linear mode of plant vibration is considered. The two-way coupling between the plant motion and the wind flow occurs through the drag force term. This coupling model is validated on a crop canopy of alfalfa whose motions have been previously analysed in great details from video recordings. It is shown that the model is able to reproduce the well-known phenomenon of honami. Moreover, the wavelength of the main coherent waving patches, extracted using a bi-orthogonal decomposition (BOD) of the crop velocity fields, is in agreement with that deduced from video recordings. The spatial and temporal main characteristics of these waving patches exhibit the same dependence on the magnitude of the mean wind velocity as in the in-situ measurements. Also they differ from the coherent eddy structures of the canopy-top wind flow. Finally, it is observed that the impact of crop motion on the wind flow is negligible for current wind speed values.