To provide a method by which cost for equipment is reduced and plants are promptly protected from disaster.

The method for protecting plants from disaster in open-field hydroponics includes; making the leaf and stem parts of the plants get out from the upper surface of a cultivation box while holding the roots of the plants inside the cultivation box made of a heat insulating material; supplying and draining a culture liquid to and from the roots inside the box to perform open field hydroponics; flipping the cultivation box upside down so as to make the cultivation box function as a roof, form a plant protection space under the roof, and place the leaf and stem parts of the plants inside the protection space to protect the plants from disaster, when disaster approaches the plants during cultivation.

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