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. Germination of achenes of both bulrushes increases with increasing daytime temperatures and when temperatures fluctuate. Regardless of storage conditions, S. robustus achenes subject to alternate freezing and thawing or constant freezing germinate better than those stored at room temperature. Under proper light and temperature cycles, S. robustus achenes show high germination rates on paper moistened with distilled water. Even small amounts of salts depress germination and seedling growth.