Minecraft wiki entry for Wheat_Seeds, associated text: Wheat seeds can be placed on farmland by right-clicking, where they grow through eight stages. When left alone, wheat seeds planted on farmland grow to become wheat crops, which can be harvested by the player. Planted seeds require a light level of 9 or greater to continue growing. If the light level is 7 or below, the crops un-plant themselves ("pop off"). It is not possible to plant seeds if the light level is too low.