As little as 2.5 cm of water over S. robustus achenes held in pure quartz sand stifles germination for at least 25 days, but the same achenes germinate normally when water levels are lowered to the sand surface. However, more S. maritimus seedlings emerge when core samples of bottom substrate are held under 4-5 cm of water than when they are merely kept moist, although the germination rate is highest when these conditions alternate. For this species, water depths of less than 10 cm have little effect on germination of achenes buried 2 cm or less in sediments. In summary, both bulrushes have adaptations for achene production, dissemination, and germination in unstable environments where water levels and salinities fluctuate and bottom sediments are exposed. The common mode of expansion of clones of Scirpus maritimus and S. robustus is by a network of creeping rhizomes and corms that are concentrated at the periphery.
Rhizomes grow in a linear pattern and bear new shoots at regular intervals.
Little, if any, seedling production occurs inside an established network of rhizomes. The vegetative life cycle of this species is about 130 days. The central portions of older annular clones often die and expose corms, roots, and rhizomes. Scirpus maritimus exhibits bud dormancy whereby some of the usually 1-5 buds can remain dormant when the corms first germinate. Like achene germination, corm sprouting and growth are negatively affected by increased water salinity.