A method for hydroponically cultivating a low-potassium vegetable in which the total cultivation period from sowing to harvest is divided into a first cultivation period, a second cultivation period, and a third cultivation period according to the vegetable being cultivated. In the first cultivation period, the vegetable is cultivated using a hydroponic cultivation fertilizer containing potassium. In the second cultivation period, the vegetable is cultivated using a hydroponic cultivation fertilizer that essentially does not contain potassium and contains magnesium. In the third cultivation period, the vegetable is cultivated using water that does not contain a fertilizer.