Silicon (Si) is the second most abundant element in the soil and is known to help in crop productivity. Si improves photosynthesis as well as remediates nutrient imbalances and abiotic stresses in plants. The impact and the importance of different sources, concentration, and supply of Si in improving the propagation of horticultural crops are limited. Thus, the present study focused on the supply, concentration, and source of Si on two important Korean strawberry cultivars ‘Sulhyang’ and ‘Maehyang’ under temperature stress. The high temperature (41 °C) resulted in oxidative stress in the form of H2O2 and O2 1− localizations in the -Si- and Si-treated plants as compared to 25 or 33 °C in both cultivars. However, Si, especially that from K2SiO3 source, had the ability to relieve the stress level. The immunoblots of two important photosynthetic proteins PsaA and PsbA showed decreased expression levels in the -Si plants under 41 °C temperature stress, whereas the expression levels were retained in the Si-supplied plants, particularly with K2SiO3 as the Si source. In both 25 and 33 °C, no changes in expressions of PsaA and PsbA were observed. Interestingly, the expression of three important stress-responsive proteins, superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT), were abundantly increased in the Si-treated plants under high-temperature stress (41 °C) and decreased in the –Si-treated plants except in those grown in 25 or 33 °C. The observed responses to silicon supply in high temperature stressed-plants indicate that Si, particularly in the form of K2SiO3, has a significant role in limiting the negative effects of high temperature stress by maintaining the photosynthetic proteins and stress-responsive proteins of the ascorbate glutathione defense mechanism. Moreover, these results also depict that Si application is a good way to maintain the health of plants at the propagation stage even under high temperatures of greenhouses. © 2017, Springer Science+Business Media New York.