I have broccoli plants that after the winter have gone to flower. gathering the flowers I get the seeds for the next sowing, and the plant must be uprooted or left to produce it again?
broccoli, like most cruciferae, are biennial plants; in spring or summer they begin to develop, producing inflorescences, those that we gather and eat for several weeks; after the winter frost the plant begins to develop a tall stem, which bears yellow or white flowers, very different from those of the inflorescences we have collected and consumed; from these particular flowers are also produced the seeds, those that you keep to sow them in the following months, and start the cycle again. After the production of the seeds, the plant perishes and dies, because it has already implemented its entire life cycle. If you had to cut the stem that bears the seeds, perhaps the plant could live longer, but it is unlikely that it will continue to constantly produce inflorescences to cut and eat, because over time it will tend to have no more resources to be able to produce the inflorescences edible; in addition to this, plants, like all living beings, have a very precise life cycle, this cycle in many plants is completely aimed at propagation, to perpetuate the species; when a broccoli plant begins to prepare for flowering, it stops producing the large and fleshy side inflorescences, because it is trying to keep reserves of water and nutrients, which will be used to produce flowers, fruits and seeds, to go to conclude its life cycle. For this reason, even if your plant were to survive for a few more weeks, it would not produce broccoli that would be interesting for consumption in the kitchen.
Cruciferae of the brassica genus have been cultivated by humans for several millennia, this long cultivation period has allowed the development of numerous hybrids and natural cultivars, some of which produce inflorescences ready for consumption in autumn, others in spring, others in summer. For this reason it is possible to have broccoli almost all year long. So if you are particularly fond of broccoli, and you want to get them in your garden for a longer period of time, try planting plants of different varieties from the one you usually use, with a development period staggered over the months, in so as to prolong the harvest.