How to Grow Sweet Onions
The key to successful sweet onion growth is giving the plants enough time to form really large bulbs. The best way to do this is to plant them in late summer or early autumn and let them grow through the winter. This means sweet onion plants grow best in climates that have mild winters. The most popular sweet onion plants for winter growing are called short-day onions, a variety that still grows well during the short days of winter. These onions tend to be hardy down to 20 degrees F. (-7 C.). Other varieties, called intermediate day, are hardy down to 0 degrees F. (-18 C.) and can survive in colder climates. If your winters are very cold, it’s also possible to start sweet onions indoors and transplant them out in the spring, though the bulbs will never get as big. Sweet onions like well-drained, fertile soil. They are heavy feeders and drinkers, so caring for sweet onions involves watering them frequently and applying regular fertilizer in the spring when the bulbs are forming. Avoid fertilizers with sulfur, as this will make the onions taste less sweet. Short day sweet onions should be ready to harvest in early to midspring, while intermediate day varieties should be ready in early to midsummer.
