How Long Do Onions Take to Grow?

Depending on the onion variety, the time it takes for them to grow to maturity differs. The time also depends on whether you started your onions from seed, sets or transplants. All onions go through the same growing stages, but times vary from 50 days to 125 days.


Onion Stages

It’s interesting to see the various stages that onions go through as they grow. Knowing these stages can help you determine when your onions are ready to harvest, no matter which variety you planted.

  • Germination – This takes place from one week to one month after planting onion seeds.
  • Leaf Growth – Two leaves grow from the seedling from 4 to 6 weeks after planting. The next two leaves form from 6 to 9 weeks after planting.
  • Bulb formation – After 7 to 9 weeks, five to seven leaves grow on the onion seedling, and a bulb forms to a size that is two times the diameter of the onion neck.
  • First stage of bulb growth– In about 3 to 3.5 months, the seedling grows eight to 12 leaves, and the bulb grows to 1-1.5 inches in diameter.
  • Second stage of bulb growth – From 3.5 to 4 months after planting, the bulb reaches from 1.5–3 inches in diameter.
  • Third stage of bulb growth – From 4 to 4.5 months after planting, the bulb diameter becomes larger than 3 inches in diameter.
  • Maturation – The onions reach full maturity after about 5 months. You can tell if your onions are mature when the onion tops tip over and start to turn yellow.

Planting Onions

You have three choices when planting your onions. Each grow at different rates, so before choosing which one to use, decide on how long you want them to grow before harvesting.


Seeds take the longest time to grow mature onions. Although you can sow the seeds directly in your garden, it will add about 8 weeks to the growing time. You can start your onion seeds indoors from 4 to 6 weeks before you expect the last frost to hasten the growth. Another option is to plant the seeds in a cold frame to protect them from the frost. When your seedlings are about 3-inches tall, transplant them to your garden.


Choosing onion transplants saves you the time and effort of starting seeds indoors. Plant them directly in your garden after any danger of frost. Most transplants take about 2 months to grow into mature onions.


The fastest way to grow onions is to use sets. Sets usually result in healthy, strong onions. Onion sets are small onions produced for replanting. You can find red, yellow and white onion sets at any gardening store. To plant your sets, press the bulbs into the soil. Cover them lightly. Space the bulbs from 3-4 inches apart in rows from 2-3 feet apart. When the onion stems fall over, your onions are mature.