After sinking, the achenes are viable for at least 2 years. Nearly all achenes are in the upper 6 cm of bottom sediments. Achenes sometimes are well represented in seed banks, even when plants do not occur in existing vegetation. Achenes germinate under conditions of relatively high illumination and temperature and low salinity in shallow water or on exposed saturated bottoms. Scirpus robustus achenes can germinate while floating.
Roots emerge only when seedlings are in contact with bottom substrates.
Scirpus robustus achenes collected late in the growing season and stored in air-tight containers for more than 5 years readily germinate. Such after-ripening and stratification occur naturally in wetlands during the winter after production. Pericarp injury by mechanical means or by acid treatments increases germination. Germination requires light yet seems little affected by photoperiod length. Darkness may induce a secondary dormancy in S. robustus achenes that may prevent their germination when buried or when exposed in heavy shade.