A Study on the Restorative Effects of Hydrangea Flower Color and Structure on Human Psychology and Physiology

Amid growing “nature deficit” associated with urbanization and indoor living, flowering plants are increasingly used to support psychological restoration. Yet evidence on how floral color and structural morphology jointly shape restorative outcomes remains limited. This study employed a within-subjects, repeated-measures design, utilizing physiological instruments and psychological questionnaires to investigate the physiological and psychological restorative benefits of Hydrangea macrophylla and to quantify the differences in restorative effects across five colors (blue, pink, white, mauve, red), two inflorescence types (mophead, lacecap), and two petal structures (single, double). Twenty-eight healthy young adults viewed 15 live hydrangea stimuli under controlled laboratory conditions. Multimodal outcomes combined objective measures—eye-tracking and single-channel EEG—with subjective measures (SD; POMS). Hydrangea exposure significantly reduced negative mood, and color and structure exerted distinct and interactive effects on visual attention and arousal. Red and mauve elicited larger pupil diameters than white and pink, while lacecap inflorescences were associated with lower cognitive load and improved attentional recovery relative to mophead. Double-petaled forms showed greater attentional dispersion than single-petaled forms. Interactions indicated that morphology modulated color effects. The mauve lacecap double-flowered cultivar (M02) showed the strongest observed restorative potential within this sample. These findings highlight the importance of integrating color and structural cues when selecting flowering plants for restorative environments and horticultural therapy, and they motivate field-based replications with broader samples and higher-density physiology.