PROBLEM TO BE SOLVED: To provide a water tank for gardening greenhouse cultivation to be used in a gardening greenhouse greatly reducing the decline of temperature in the nighttime in the gardening greenhouse and retaining the temperature suitable for crop cultivation at a low cost and with saved energy by reducing the energy of petroleum oil and gas to be used for retaining the temperature； and a method for raising plants by using the same.SOLUTION: The water tank 100 for gardening greenhouse cultivation is set within the gardening greenhouse 1. The water tank 100 includes a top surface part 2 and a body part 5 connected under the top surface part. The water tank 100 is filled with a liquid heat medium L and sealed. A cultivation bed setting part 21 for setting a cultivation bed 31 is disposed on the top surface part. The capacity X for loading the liquid heat medium is at least 1% of the capacity Y of the gardening greenhouse 1.
