PROBLEM TO BE SOLVED: To provide a method for cultivating purple loosestrife, which contributes to lakefront vegetation having no problem in terms of appearance and functions. SOLUTION: This method for cultivating purple loosestrife comprises the following processes: a process of sowing the frozen seeds of purple loosestrife in a germination tray charged with culture soil, a process of dipping the germination tray in water, a process of putting the germination tray in a germination vessel to make the seeds germinate, a process of taking out the germination tray from the germination vessel to dip it in water, a process of transplanting the seedlings having true leaves to a cell tray, a process of dipping the cell tray in water, a process of transplanting the grown seedlings to a pot after a prescribed period elapses, and a process of dipping the pot in water.
