Onions form bulbs in response to changes in day length, but different varieties have different "trigger points" that stimulate bulb formation. Short day onion varieties start to form bulbs as soon as day length exceeds 10 to 12 hours, but long day onions won't start to bulb until days are 14 to 16 hours long. Ideally, you want the onions to keep growing as long as possible before lengthening days trigger them to bulb, so different varieties work in the southern, central, and norther regions.

The sweetest onions are short day onions that grow best in mild-winter climates. Short day onions mature in about 80 days when planting in the spring. Short day onions don't store well because they contain so much water. After harvest keep them in the fridge. Try the Red Creol onion!

Intermediate day onions produce a beautiful onion with a balanced, spicy sweet flavor. When properly cured they will store for months.These are sometimes referred to as day-neutral varieties because they can be grown almost anywhere. Try the Candy Hybrid onion!

Long day onions grow best in the North region. These onions will form hard, pungent flavor that store for a very long time. Many small specialty onions grow best in northern climates. Try the White Spanish onion!