During the vegetative phase of barnyardgrass (Echinochloa crusgalli (L.) Beauv.) development, the leaves, axillary buds (tillers) and permanent root system were initiated and developed. First adventitious roots appeared on the 6th day after germination. Internode elongation, which was coincident with a change from a vegetative phase to a reproductive phase of the plant, was observed in the field about 30 days after germination. At this time the main stem had 4–5 maturing leaves. Typically, barnyardgrass formed 8 leaves on the main axis from primordia which were initiated during the first two weeks after germination. The first tiller primordium appeared in the axil of either the 1st or 2nd leaf on the day of emergence from the soil. In the field, tillering was observed from the twelfth day. Heading began on the 40th day and the first mature seeds were formed about 64 days after germination.