Technical Abstract: The number and identity of plant species varies by season and location. We sampled pastures on five grazing farms (four dairy, one beef): two in New York, two in Pennsylvania, and one in Maryland. Pasture plant composition was measured on five to seven pastures in the spring (April-May), summer (July) and autumn (September-October) for three years. We found 224 plant species in all, with 108-148 species on a single farm. The fewest species were found in the spring (140), and the most in the summer (199). In the autumn we found 180 species. Nine species were found only in the spring, 29 only in the summer, and 12 only in the autumn, while 121 were found throughout the growing season. Major forage species were all found throughout the year, though abundance varied with season. Seasonal changes in species composition with season and state affect forage quality and availability. Understanding these differences can aid management.