Broccoli is a hardy vegetable that develops best during cool seasons of the year. Two crops per year, spring and fall, are possible in most parts of the country. It belongs to the crop family Brassica oleracea, which includes cabbage, Brussels sprouts, cauliflower, and other greens.
When you see a flower head beginning to form in the center of the plant, check its growth every day. Ideally, you harvest broccoli while the tiny buds are tightly closed. If the buds begin to swell or show yellow (the flower petals), cut the head from the stem right away, no matter how small it is, because the opening buds have a mealy texture.
The reason plants flower and go to seed too early is usually because they've been starved. Either they have not had enough water or not enough food.
Another possibility, especially with broccoli, which is cold loving, is that it's just too hot for your plants. Most broccolis in hot areas like to be sown or planted in autumn so they can get established and produce during winter or early spring.
The best way to prevent broccoli flowers from happening too early is to keep the soil the broccoli is planted in cool. Another tip for growing broccoli in hot weather is to water frequently. The cool water will help keep the soil cool as well and will stop bolting broccoli.
The bright yellow broccoli flowers are edible and delicious. If you miss harvesting at the tight bud stage, you can still harvest broccoli, even with the flowers open. Broccoli flowers can be eaten raw or cooked. Use them as an edible garnish or include them as a nutritious and attractive addition to any salad. Completely opened flowers will wilt when steamed, but partially opened buds retain their shape. Broccoli flowers have a pleasant, mild flavor. Some specialty markets sell yellow broccoli flowers in the produce section as a delicacy item.
There are three commonly grown types of broccoli. The most familiar is Calabrese broccoli, often referred to simply as "broccoli", and it is named after Calabria in Italy. It has large green heads and thick stalks. It is a cool season annual crop.
Sprouting broccoli has a larger number of heads with many thin stalks. Purple cauliflower is a type of broccoli cultivated especially in the Mediterranean countries. It has a head shaped like cauliflower, but consisting of tiny flower buds. It sometimes, but not always, has a purple cast to the tips of the flower buds./AgroWeb.org