How long do onions take to grow?

The length of time it takes for onions to grow is 20 to 30 days for green onions and 100 to 175 days for dry bulb onions. When the leaves lose their color and begin to fall or droop, the onions have reached maturity.

Planting onions from seeds requires about five months for full development. Small onion bulbs, or sets, are easier to cultivate than seeds or transplants, and they mature in about two months. After planting in cool weather, the onion tops grow, and when the weather warms, the bulbs develop. The length of day and the temperature determine when bulbs begin to grow. If temperatures hover between 30 and 40 degrees Fahrenheit, then the length of the growing period increases.