Tomatoes grow best if daytime temperatures range between 70 F / 21 C and 85 F / 29 C. While tomato plants can tolerate more extreme temperatures for short periods, several days or nights with temps outside the ideal range will cause the plant to abort fruit set and focus on survival. According to the University of NV, "...temperatures over 104 F / 40 C for only four hours can cause the flowers to abort."