Oatstraw is the green top of the oat plant, harvested when the seed is at the milky stage, before it's fully ripe. Cultivated for over 3,000 years, oats were not an intentionally cultivated grain. A happy accident, it was originallyÊconsidered a weed among other crop grains. However, its tenacious nature and and wide tolerance for growing conditions led to eventual appreciation. It can thrive through stretches of poor growing conditions while other crops struggle.