The present work were conducted in 2018/2019 and 2019/2020 seasons at Kaha Vegetable Research Farm, Qaliobia Governorate, Horticulture Research Institute (HRI), Agriculture Research Center (ARC), Egypt, under greenhouse condition. Marcella hybrid was used to investigate the influence of foliar spraying application with salicylic acid (SA) 50 ppm, potassium silicate 50 mg/l and selenium (Se) 5 mg /l on squash plants as well as the control treatment (tap water) on vegetative growth, yield, fruit quality and chemical constituents. Results cleared that, Plant height; number of leaves per plant, leaf area, and chlorophyll content are all improved by potassium silicate foliar spraying when compared to other foliar treatments. the heights values of average fruit weight, early and total yield and fruit quality obtained from spraying squash plants with potassium silicate without significant differences with salicylic acid. However, foliar spraying of the plants with potassium silicate, selenium and salicylic acid increased fruit quality (TSS, ascorbic acid and total sugars) of squash fruits. Generally, it may be suggested that the best way to produce high vegetative growth, yield, and high-quality fruits from squash plants grown in greenhouses is to spray 50 ppm of potassium silicate three times during the season.