12 to 24 hours. In this way, water can be fully absorbed, which is helpful for faster and more sufficient water penetration, so as to promote the germination and growth of Eupatorium odoratum seeds. When soaking in water, clean water at room temperature should be used to avoid using overheated or supercooled water to soak seeds. In the process of soaking seeds, water should be changed regularly to maintain good cleanliness and water quality.