This research was conducted to determine whether calcium could extend flower life in $Hibiscus$ $syriacus$ and to characterize the relationship between the calcium level and flower senescence. The effects of calcium supplied by fertigation in nutrient solution, at two levels (0 and 3 mM; Ca-0 and Ca-3, respectively), or as a leaf spray (LS) or flower spray (FS) of 45 mM $CaCl_2$ on flower life were investigated. With increasing calcium, significantly higher growth characteristics were observed. Flower life was extended by more than 8 h (15%) by Ca-3 fertigation compared to sample without calcium. Flower life was extended by 9.6 - 11.3 h with the application of a FS together with Ca-3 fertigation. There was a significant relationship between calcium application and temperature for flower life. When temperatures were low, flower life was extended more effectively by calcium treatment. However, when temperatures were increased, calcium treatments had less effect. Increasing the supply of calcium increased the calcium content in flowers, but decreased their magnesium content. The distribution of calcium in senescing petals was observed using a multi-photon imaging system with fluo-4 acetoxymethylester (Fluo-4/AM) as a fluorescent indicator for calcium. At the full flower opening stage, calcium was compartmentalized in organelles in calcium-treated petal cells and showed a strong fluorescence. Fluo-4/AM fluorescence decreased during flower senescence, but compartmentalized calcium was maintained in calcium-treated petal cells ever at full senescence. In untreated petal cells, fluorescence was lower and no compartmentalization of calcium was observed at 24 h after full flower opening. Peroxidized lipid levels increased significantly during flower senescence, when visual symptoms appeared. Calcium treatment decreased lipid peroxidation. In conclusion, we suggest that exogenous calcium treatment can raise calcium levels in the petals of $H.$ $syriacus$ petals, maintain calcium compartmentalized in organelles, alleviate lipid peroxidation in petals, and ultimately, extend flower life.
