The vegetable called broccoli found at markets is the immature flower heads of the plant Brassica oleracea var. italica. Broccoli is related to cabbage and other members of the cole family. High in vitamin A and D, broccoli makes a healthy addition to the vegetable garden. Broccoli grows during the cool weather in spring and fall. In cool climates, broccoli grows well in summer.

The vegetable broccoli is the immature flower heads harvested before they bloom.

Seed Germination

Broccoli is an annual vegetable plant. The first step in the growing season is seed germination. Start broccoli seeds indoors in individual 3-inch pots six weeks before the last spring frost date. Broccoli seeds take one to two weeks to germinate. Keep broccoli seeds at 80 degrees F during germination. Use a heating pad under the seed flat, or keep the seeds in a greenhouse where the temperature is consistently 80 degrees F.

Plant Development

Seedling development takes three to four weeks after the seeds germinate. During seedling development, broccoli plants develop roots and their first leaves. Once the seedlings emerge from the soil, remove them from the heating pad and place them in an area where the air temperature is between 60 and 65 degrees F. Keep broccoli seedlings indoors until they are four weeks old. Water the seedlings by soaking each pot when the top of the soil begins to feel dry. Always use pots with drainage holes in the bottom. Standing water around the young, developing broccoli roots causes rot and seedling death.

Early and Mature Harvest Flowering Tops

Broccoli develops a stalk and mature leaves before producing the flowering top. Broccoli plants mature for harvest in 50 to 65 days after planting. Transplant broccoli as early as possible in spring after the last frost date and when the soil temperature warms to 60 or 65 degrees F. Use a soil thermometer to determine the soil temperature before planting out the seedlings. Keep the soil damp around the developing broccoli plants and remove weeds by hand.

Harvest and Seed Collection

The last stage of growth before harvest is the development of flower heads. Harvest broccoli when the flower heads are 6 to 8 inches across and compact, with tightly closed green buds. Developing broccoli heads can be harvested at any point. The final stage of broccoli development is the flower and seed development. Any broccoli that is allowed to go to seed will not be harvestable. Allow a few plants to go to seed for next year's crop. Harvest the seed pods when they dry and turn brown on the plant. Till the old plant material into the soil in the fall after the last harvest.