Downy mildew on onion (Allium cepa L.) is of great economic importance because of its impact on yield and quality. Natural biostimulants such as propolis play a vital role in enhancing growth and productivity by activating physiological and biochemical processes in plants, increasing water and nutrient uptake, and enhancing productivity. Our study aimed to evaluate the effects of foliar spray treatments with nano-propolis and potassium silicate on onion growth, dry bulb yield, its components, and quality. Nano-propolis was applied at concentrations of 1 and 2ml/L, potassium silicate 2 and 4ml/L, both individually and in combination, and distilled water as a control treatment. The results showed that plants sprayed with different concentrations of nano-propolis or potassium silicate showed high resistance to downy mildew; increased vegetative growth, yield and bulb quality; and higher levels of nitrogen, phosphorus, potassium and protein. The combined foliar application of 2ml/L of nano-propolis + 4ml/L of potassium silicate enhanced resistance to downy mildew and all measured parameters, including bulb weight, diameter and yield, compared to other treatments. In conclusion, foliar spraying of nano-propolis and potassium silicate is an eco-friendly and beneficial approach for sustainable crop production.