Ammophila arenaria is a stout perennial grass with horizontal and vertical rhizomes. Horizontal rhizomes anchor the young plants and produce new shoots around the parent plant. Vertical rhizomes develop, branching from a horizontal rhizome, as sand accumulates around plants. Several aerial shoots or tillers per node arise from the vertical rhizome to form dense tufts.
Shoots grow most vigorously in spring when leaf production exceeds leaf senescence. In autumn the latter predominates. Growth slows during winter but never ceases entirely (Huiskes 1979a). On dune systems in Sweden, the average yearly above ground biomass production is 400 grams per square meter (Wallen 1980).
A. arenaria is highly adapted to sand accretion. It can withstand burial by as much as one meter per year. Sand burial promotes both leaf elongation and development of vertical rhizomes from axillary buds on the horizontal stems (Ranwell 1959). Internode length of vertical rhizomes varies according to the amount of sand burial and indicates seasonal sand accretion (Huiskes 1979a).
Inflorescences are initiated in autumn of the second year after germination and mature in May or June. Flowering occurs from May to August. In Europe, anthesis occurs in July and August (Huiskes 1979a) but has been reported as early as May (Munz and Keck 1973). Mature fruits are dispersed in September. Seeds germinate the following spring. Viability of seeds is low. Seedling survival is low as a result of desiccation, burial, and/or erosion.
Reproduction is primarily vegetative by rhizomes. Rhizome fragments are dispersed along the shore by wind and water (Wallen 1980).
A. arenaria usually invades from the upper beach. There, rhizome fragments of the grass are washed ashore, buried, and sprout. Rapid vertical growth of the grass initiates dune formation, and the grass spreads rapidly in all directions by horizontal rhizomes.