To grow onions from onions, follow these steps. First, select a site that gets at least six hours of sunshine with soil that has good drainage and a pH of between 6.0 and 7.5. Then purchase the onion sets and then start preparing the area you selected. Remove any traces of weeds and deter cutworms and maggots by adding parasitic nematodes. In February, the onion plant sets four inches apart in rows and one foot apart. Feed the onions with a seaweed-based fertilizer to provide the macronutrients required by the plant. Finally, give the onions the appropriate time to reach their maximum size and harvest them between August and September.