(1) Germination stage
The germination period is from seed germination to the appearance of the first real leaf (heartbreak). Under suitable conditions, seeds with strong vitality will germinate for 7-9 days. Seed germination must have suitable temperature and humidity conditions and good ventilation. After the seeds germinate, the radicle first grows, then the hypocotyl elongates and the cotyledons are pushed out of the ground. After the cotyledon unfolds, the growing point breaks and the first real leaf grows.
(2) Seedling stage
From the first true leaf to the big bud, it is the seedling stage. There is only vegetative growth in the early stage of seedlings, mainly vegetative growth in the later stage, and reproductive growth begins at the same time. It usually takes only 45~50 days to complete the seedling stage in summer, but it often takes 55~65 days to get through the seedling stage in winter and spring due to low ambient temperature, weak light and slow plant growth.
At the early stage of seedling, the root system grows rapidly, and a large number of lateral roots are formed while the main roots grow, which is beneficial to absorb nutrients in the soil. The growing leaf area accumulates nutrients through photosynthesis, which provides material basis for flower bud differentiation. Seedling growth at this stage will affect flower bud differentiation and the first inflorescence node. When the seedbed temperature is too high, the seedlings turn white, the flower bud differentiation is delayed and the inflorescence internodes become longer. When the temperature of seedbed is too low, it is easy to form so-called "old seedlings", that is, the growing points no longer differentiate and the plants stop growing. This kind of seedling is meaningless in production.
When the seedling has 2~4 true leaves in morphology, flower bud differentiation begins until big buds appear, which is the late stage of the seedling. Generally, when the accumulated temperature of seedlings reaches 570 ~ 600℃, flower bud differentiation begins. At this time, the growing point has differentiated into 8~9 true leaves, and then the leaf differentiation stops, and the growing point forms flower primordium and differentiates into flower buds. In winter, when the seedlings are long, they are often divided at one time. In order not to affect the flower bud differentiation, in production, before the flower bud differentiation, that is, when the two leaves of the seedling are combined, the seedling is separated. After new roots and slow seedling growth, plants began to differentiate flower buds. By the time the big flower buds are ready for planting, the seedlings have differentiated into three inflorescences and entered the flowering stage.
(3) flowering and fruit-setting period
The flowering and fruit setting period is from the big bud stage to the first ear and fruit stage of tomato. At this stage, plants are in the transition stage from vegetative growth to vegetative growth and reproductive growth. The length of flowering period is closely related to variety characteristics, cultivation environment and other factors. The flowering period of early-maturing varieties is more concentrated and the experience time is shorter than that of middle-late-maturing varieties. The flowering period of the same variety in high temperature environment is shorter than that in low temperature environment.