In computer graphics and engineering many classes of complex objects can be designed with L-systems. We present a concept for enhancing timed and parametric L-systems with physics. This simplifies considerably the physically correct design of certain classes of computer animations or technical objects modelled by production rules. The focus is on structural extensions in timed and parametric L-system theory necessary for constraint propagation management for the treatment of hierarchical objects and on physics enhanced grammar-language extensions. The proposed concept is illustrated with a design model incorporating the statics of arbitrary tree structures.