Cutting off the broccoli heads along with 25 cm of the edible stem portion should be carried out manually to maintain the quality of the vegetable. Make use of a sharp knife to cut the head stem, above from the below head. Most of the cultivar has side-shoots that allow other heads to develop, even after the main head is harvested. This also helps in getting production at different intervals of time. To get a good quality of heads, the best time for harvesting is early morning.
Source: