Leaves of leather fern are used as a foliage plant and Mottled Yellowing Syndrome (MYS) has been occurring on leaves cultivated in protected greenhouses at Hachijo Island since the 1990s. Experiments with different shading levels and soil moisture levels were carried out to develop cultivation methods that will prevent the occurrence of MYS. Relationships between the greenhouse environment and the occurrence of MYS were examined and the following results were obtained.The temperature of air, the canopy surface, and soil in the greenhouses were affected not only by shading levels but also by the color of the shading net. Air and canopy surface temperature decreased with an increase of shading rate with blue nets, however, temperatures under black nets were quite high due to the high surface temperature of the nets, which caused a high occurrence of MYS.Numbers of leaves decreased with an increase of shading level, but the leaf size increased. Chlorophyll content of the leaves increased with shading levels too.An optimum greenhouse environment to increase leaf size, leaf number, and chlorophyll content was obtained by a using a blue net with a 55% shading rate and the soil water potential controlled to less than 0.016MPa.MYS occurrence is increased by high temperature stress of the plant rather than high solar radiation in greenhouses. Also, MYS occurrence was decreased by frequent irrigation.MYS occurrence (%) can be estimated by degree days over 34°C of maximum air temperature for well-irrigated greenhouses, and by 1.5 times the degree days over 32°C for less-irrigated greenhouses. Farmers can manage the greenhouse environment to reduce MYS damage by applying these results.Greenhouses devoted to leather fern cultivation should be shaded (around half the amount of sunlight compared to outside) and should be controlled to keep good ventilation and soil moisture by frequent irrigation, which provides a desirable canopy surface-, air- and soil temperature, resulting in reduction of MYS damage and improvement in productivity and quality.