PROBLEM TO BE SOLVED: To decrease energy consumed to heat the inside of a greenhouse, while getting the same to be comfortable environment for plants as their growth environment by effectively utilizing heat energy of superheated steam and reduce plant cultivation costs.SOLUTION: The method comprises: heating air in a greenhouse 11 by supplying superheated steam inside the greenhouse 11 while supplying carbon dioxide gas inside the greenhouse 11 in addition to the superheated steam to make mixture gas in which the superheated steam is mixed with the carbon dioxide gas； and stagnating the mixture gas containing the carbon dioxide gas in a lower layer inside the greenhouse 11 and allowing plants inside the greenhouse 11 to be maintained in a heated state and to grow.【課題】過熱水蒸気の熱エネルギを有効に利用して、植物の生育環境を快適な環境としながら温室内を加温するために消費するエネルギーを少なくして植物の栽培コストを削減する。【解決手段】温室１１内に過熱水蒸気を供給して温室１１内の空気を加温すると共に、過熱水蒸気に加えて温室１１内に炭酸ガスを供給して、過熱水蒸気に炭酸ガスを混合してなる混合気体とし、炭酸ガスを含む混合気体を温室１１内の下層に停滞させて温室１１内の植物を加温状態に保持して生育させる。【選択図】図１
