PROBLEM TO BE SOLVED: To provide an apparatus and a method capable of adjusting the temperature of a medium at low cost. SOLUTION: The horticultural culture medium heat retaining device according to one aspect of the present invention is a horticultural culture medium heat retaining device arranged in a medium for growing a plant, and is sealed by a transparent member that can transmit sunlight and the transparent member. A main body having an accommodation space formed so as to be capable of accommodating a fluid. [Selection diagram] Fig. 4【課題】培地の温度を低コストで調節可能な装置及び方法を提供する。【解決手段】本発明の一側面に係る園芸培地用保温装置は、植物を育てる培地に配置される園芸培地用保温装置であって、日光を透過可能な透明部材と、前記透明部材により密封され、流体を収容可能に形成された収容空間を有する本体部と、を備える。【選択図】図４
