Allometric biomass allocation theory and optimal partitioning theory are the most important theoretical frameworks for explaining and predicting plant biomass allocation patterns. But their focus on equilibrium conditions does not advance our understanding of transient allocation patterns. To address this limitation, we develop a heuristic approach with a quantitative metric to theoretically analyze transient patterns of plant allocation of photosynthetic products to different plant organs. The approach is also used to ask how various factors can drive transient patterns. A case study is analyzed, showing how periodic perturbations of transient patterns of plant leaf and stem biomass can decrease or increase in response to plant height, crown diameter, and projected crown area. The predictions are consistent with global data on forest plants. The approach here addresses the limitations of optimal partitioning theory by revealing the variation in plant photosynthetic partitioning over short time scales. Given the central role of plant biomass allocation patterns for both empirical and theoretical studies, there is a large scope for applying this approach to improve estimations of carbon stock, and stabilized yields in forest management.