Delayed reproduction in soils with low phosphorus (P) availability is common among annuals, in contrast to the accelerated reproduction typical of other low-nutrient environments. Nord et al. present a two-resource dynamic allocation model of plant growth and reproduction for Arabidopsis thaliana that incorporates growth, respiration, and carbon and P acquisition of both root and shoot tissue, and considers the reallocation of resources from senescent leaves. The model suggests that delayed reproduction in response to low P availability may be reduced in plants adapted to environments where P mobility is greater.