By late August the mature fruits have turned brown, and in early September they split open and the seeds fall to the ground. The seeds are relished by many small mammals, such as kangaroo rats, and by birds, such as prairie grouse. The few seeds that remain uneaten are blown along the soil surface until they are covered, a thick seed-coat protecting them from the abrasive sand. Buried seeds can remain viable for 20 years and can germinate if sand movement eventually brings them close to the surface. For seeds to germinate and for the roots of seedlings to reach a depth where moisture is constantly available, blowout sand must remain damp for at least two weeks, conditions that usually occur only in one of eight or 10 years, limiting seedling establishment.
Seedlings are rare even where adult plants are present and seeds are abundant.
The Sandhills is the largest area of sand dunes in the Western Hemisphere, occupying more than 12 million acres in north-central Nebraska. The dunes range in height from a few feet to more than 300 feet. Major periods of dune movement occurred 8,000 to 5,000 years ago, with more recent periods of lesser dune reactivation. In the most recent centuries, climatic conditions have been wet enough for the dunes to support sufficient vegetation to keep them stable. Nevertheless, dune soils are poorly developed because of the constant erosion and deposition of sand.