In the Northern and Central States, beech flowers appear in late April or early May when the leaves are about one-third grown; the species is monoecious. The flowers are quite vulnerable to spring frosts. Male flowers occur in long-stemmed heads; female flowers in clusters of two to four (40). Beechnuts require one growing season to mature and they ripen between September and November. Two or (rarely) three nuts may be found within a single bur. The first nuts to fall are usually wormy or aborted. Seed fall begins after the first heavy frosts have caused the burs to open and is completed within a few weeks. Some empty burs remain on the trees throughout the winter.