Aligning auxin supply to developmental demand in adventitious rooting

Adventitious root (AR) formation is the developmental process that makes vegetative propagation possible, underpinning forestry, horticulture, and the clonal multiplication of elite and hard-to-propagate genotypes. Despite a detailed understanding of auxin's stage-specific roles across the rooting program, propagation practice still treats auxin supply as a quantity to set rather than a profile to match. We argue that this produces a temporal mismatch between auxin supply and developmental demand: the available evidence shows that exogenous auxin availability frequently declines before the stages it should support are complete, particularly in slow-to-root and recalcitrant species, where developmental timelines are longest. New delivery tools, such as slow-release conjugates, encapsulation systems, and selective auxin agonists, now make time-structured delivery profiles feasible, but realizing their potential requires a different starting point. Rather than optimizing auxin dose empirically against rooting outcome, the field should characterize the spatiotemporal auxin demand curve across AR stages and design delivery profiles to match it. We outline the conceptual framework for this shift and the experimental approaches now available to support it.