The minimum temperature required for tomato seeds to begin germination is 13°C, although some cultivars can germinate at 10°C. The optimal temperature for germination is 20 – 25°C.
Tomato seeds germinate best in darkness, but there are cultivars whose seeds cannot germinate in light. The optimal temperatures for the growth and development of tomatoes are 20 – 25°C during the day and 13 – 17°C at night. A desirable difference between daytime and nighttime temperatures is around 7°C. The sensitive phase for tomatoes regarding temperature starts 8 days after the cotyledons open and lasts about 2 weeks.
From pollination to the technological ripeness of the fruit, it takes 7 – 9 weeks, depending on the cultivar, the position of the inflorescence on the plant, and the environmental conditions. In the first 2 – 3 weeks, the fruit grows slowly, reaching only 10% of its final size. In the next 3 – 5 weeks, it achieves its full size. In the last 2 weeks, fruit growth slows down again, but important metabolic processes occur, allowing the fruit to reach full ripeness.
The most favorable temperature for tomato development is 15 – 20°C at night, with daytime temperatures being about 7°C higher. The red pigment does not form below 16°C, and uneven fruit coloring can result from unequal heating.
