Context: Defensive action of plants against biotic and abiotic stresses has been augmented by silicon (Si). Spinach (Spinacia oleracea L.) is a nutritious leafy vegetable that is a cold-tolerant but heat-sensitive crop.Aims and methods: The ability of exogenous application of Si (0, 2, 4 and 6 mmol L−1 in the form of K2SiO3) to alleviate heat stress in spinach cv. Desi Palak was investigated. After an acclimatisation period, plants were grown with or without heat stress for 15 days, followed by Si treatment for 25 days. Plant growth and physiology were assessed at 65 days after sowing.Key results: Heat stress significantly inhibited plant growth, water status and photosynthesis, soluble sugar and protein contents, and osmolyte status in spinach leaves, but increased electrolyte leakage, activities of antioxidant enzymes, and proline content. Application of Si alleviated heat stress by enhancing water status, photosynthetic pigments, soluble proteins and essential minerals, and by reducing damage of the plasma membrane. The accumulation of osmolytes counterbalance the osmotic stress imposed by heat.Conclusions: Silicon plays a vital role in alleviating effects of heat stress by improving water status and photosynthetic rate, and accruing osmoprotectants other than proline.Implications: Exogenous application of Si is an efficient strategy to boost tolerance of spinach plants to heat stress, having significant impact on growth and productivity of spinach at higher temperatures.