Greenhouse tomato is the most important vegetable crop in Canada.However,the fruit disorder problem,such as blossom end rot (BER),occurred frequently,especially during summer,negatively affecting tomatoes growth and yield.This study was undertaken to investigate the effects of Ca and K,and weather conditions on fruit quality (BER),to optimize the mineral nutrition and environment control for greenhouse tomato production under hot summer climatic conditions.The results show that the 200 mg Ca2+L-1 in nutrient solution was sufficient during hot summer weather.Increasing Ca2+ concentration in nutrient solution may not reduce BER,but increase the incidence of BER.Increasing potassium concentration in nutrient solution may increase solution EC sharply,and may result in high incidence of BER.Sharp change of environment factors may lead to large high incidence of BER.