Although plants are mostly seen as static, they are constantly moving to adapt to changes in their stature and to their environment. Gravity and light, among others, are major factors that sculpt the shapes of plants. Plants tend to grow in the direction of the light to get access to their energy resource. At the same time, however, they need to maintain their balance and control their posture. In a recent study, we showed that postural control is regulated by two types of perception: graviception and proprioception. We extend that study to include light perception in order to obtain a unified description of plant tropism. As the system is highly dynamic, a model is required in order to evaluate hypotheses against experimental data. Our results show that the direction of plant growth is determined by the combined influence of light and gravity, whereas postural control is still regulated by gravity and proprioception.