Based on 1 cup of onions, spring or scallions (includes tops and bulb), raw
Read More http://nutritiondata.self.com/facts/vegetables-and-vegetable-products/2509/2#ixzz3gppOgD2Y
To prevent weeds from competing with the scallions' root space, you can plant them on black plastic. If you don't have access to black plastic, you can plant them into the ground, or in a flat in a greenhouse. Each scallion is one plant and will take up very little space, so you can broadcast the seed when growing from seed or transplant into the ground with an inch or two between each plant to prevent thinning.
Harvesting scallions is pretty simple. You can harvest them at any stage but you will get more out of one scallion if harvested when the bottom of the plant is as thick as your pinky. To harvest, pull the plant out by grasping the very bottom of the greens right above the surface. Rinse the roots off and carefully pull the outter most layer off to pull off the dead leaves and ensure a clean scallion. Rinse the leaves as well before consumption.