Despite the common use of the blooming metaphor, its floral
inspiration remains poorly understood. Here we study the physical
process of blooming in the asiatic lily Lilium casablanca. Our observations show that the edges of the petals wrinkle as the flower
opens, suggesting that differential growth drives the deployment
of these laminar shell-like structures. We use a combination of
surgical manipulations and quantitative measurements to confirm
this hypothesis and provide a simple theory for this change in the
shape of a doubly curved thin elastic shell subject to differential
growth across its planform. Our experiments and theory overturn
previous hypotheses that suggest that blooming is driven by differential growth of the inner layer of the petals and in the midrib
by providing a qualitatively different paradigm that highlights the
role of edge growth. This functional morphology suggests new
biomimetic designs for deployable structures using boundary or
edge actuation rather than the usual bulk or surface actuation.