We’re going to tell you everything you need to know to grow onions from seeds, including how to read the seed packets, pick the right variety for your area, and know when to move them to the garden. If you’ve wanted to learn how to grow onions from seed, you’re in the right place.
I’m excited to be able to have Melissa K Norris on this episode of the Pantry Chat. We’ll talk about how to grow onions from seeds, why you might want to, when to start them indoors, and even how to take care of them in the garden.
You might also want to read our post on how to properly cure and store onions after you pick them from the garden.
Growing onions from seeds allows you to expand your variety options beyond what’s available as onion sets or transplants With seed, you can choose from over 125 different onion varieties suited to your climate and cooking needs. However, onions grown from seed take patience as they require a longer growing time.
In this article, we’ll look at the full timeline of growing onions from seed You’ll learn
- How the onion growth stages progress over time
- Factors that speed up or slow down onion growth
- When to start seeds indoors vs direct sowing
- Average days to maturity for common onion types
- Tips for maximizing growth rate
Understanding the onion growth timeline helps ensure you’ll harvest a healthy crop. So let’s dive in and discover how long it really takes to grow onions from seed!
Onion Growth Stages
Onions go through distinct phases as they journey from seed to mature bulb. The key stages are:
Germination – Seeds sprout and seedlings emerge. Takes 10-15 days.
Leaf Growth – Foliage expands as roots develop. Takes 4-6 weeks.
Bulb Formation – Swelling at the base signals bulb growth. Takes 6-10 weeks.
Bulb Maturity – Onions plump up. Takes 2-4 weeks.
Foliage Dieback – Leaves turn yellow and fall over when bulbs are ripe. Takes 1-2 weeks.
Curing – Harvested bulbs are dried for storage. Takes 2+ weeks.
Total time from seed to harvest spans 13-22 weeks depending on variety. Then curing adds more time before onions can be eaten or stored. Proper curing is crucial for long term storage.
What Affects Onion Growth Speed?
Multiple variables determine how quickly onions progress through each phase:
Onion Type – Short-day varieties grow fastest. Long-day onions take longer.
Climate – Warm climates with long growing seasons speed up growth.
Soil Quality – Rich, moist, well-drained soil enables rapid growth.
Sun Exposure – Full sun is better than partial shade.
Seedling Health – Preventing disease, pests, and stress optimizes growth.
Proper Care – Watering, fertilizing, and weed control make a difference.
Spacing – Avoid overcrowding to reduce competition for resources.
When to Start Onion Seeds
You can either start onion seeds indoors or direct sow into the garden. Indoor starting gives you more control but takes extra time and supplies.
Starting Indoors
Onions grow slowly as seedlings, so indoor starting should begin 10-12 weeks before your last expected spring frost. This gives seedlings enough time to mature before being transplanted outside.
Use a seed starting mix in containers at least 2 inches deep. Cover seeds lightly, about 1⁄4 inch deep. Grow lights will boost growth. Transplant outdoors when seedlings are pencil-thick.
Direct Sowing Outdoors
Sow seeds directly in the garden 4-6 weeks before your average last spring frost date. This works well for short-day varieties in warm climates.
Plant seeds 1⁄2 inch deep and 1 inch apart in rows 12-18 inches apart. Thin seedlings to 2-4 inches between plants once they sprout.
Direct sowing avoids transplant shock but doesn’t allow for as much control over growing conditions.
Onion Seed to Harvest Timeline
Here is a breakdown of approximately how long popular onion varieties need from seed sowing to maturity:
Short-Day Onions
- Start: Early fall (warm areas) or early spring (cool areas)
- Days to maturity: 95-110 days
- Total time: 13-16 weeks
Short-day onions are fastest, making them ideal for southern gardeners. Examples: ‘Texas Early White’, ‘Southern Belle’, ‘Grano’.
Long-Day Onions
- Start: Late winter (all areas)
- Days to maturity: 100-120 days
- Total time: 14-17 weeks
Long-day onions take the longest to reach maturity. They’re recommended for northern regions. Examples: ‘Copra’, ‘Wethersfield’, ‘Patterson’.
Intermediate-Day Onions
- Start: Late winter (all areas)
- Days to maturity: 110-115 days
- Total time: 15-16 weeks
Intermediate-day onions fall between short and long-day types. Examples: ‘Early Yellow Globe’, ‘Red Wing’, ‘Superstar’.
Bunching Onions
- Start: Early spring
- Days to harvest: 50-70 days
- Total time: 7-10 weeks
Bunching onions are fast growers harvested immature before bulbs form. Examples: ‘White Lisbon’, ‘Evergreen White Bunching’, ‘Parade’.
Boosting Onion Growth Rate
Here are some tips to help your onions reach maturity as quickly as possible:
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Select short or intermediate-day varieties suited to your climate.
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Start seeds indoors to give plants a head start on growth.
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Transplant into warm, loose soil enriched with compost or manure.
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Water consistently to keep soil evenly moist but not soggy.
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Fertilize every 2-3 weeks with a balanced organic fertilizer.
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Mulch to retain moisture and reduce weeds.
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Control pests like onion maggots which slow development.
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Harvest promptly once bulb maturity is reached.
Patience and attentive care during the long growing period will help your onion seeds produce a bountiful harvest. Trust the process and you’ll soon enjoy homegrown onions!
When To Start Onion Seeds
You’ll often see the recommendation to start onion seeds 10-12 weeks before your last frost date.
From what Melissa has seen, she needs to start onion seeds about 16 weeks before the last frost date for them to get to about the same size as onion sets she buys.
We both plant our onions in early spring because that’s when they grow best where we live.
If you live in a warmer area, you can start seeds indoors or plant them directly in the garden in late fall or early winter for a harvest in late spring.
Pelleted Seeds or Loose Seeds
When ordering seeds from a catalog or online seed source you may notice a “pelleted seed” option. These work well, however, Melissa hasn’t noticed any difference in germination rate or growth.
Find types that do well in your climate is the most important piece of advice she can give you (more on this below).
Typically speaking, most seeds can successfully be grown even well past their listed “expiration date”. It is important to know that these dates are just suggestions for the germination rate, or the number of seeds that will actually grow.
Melissa has found that the expiration dates are more accurate for onion seeds, though. If you’re planting onions with older seeds, she says to plant twice or three times as many, just in case they don’t germinate.
When it comes to growing onions, many people just think of yellow, purple, or sweet onions. These are all types of onions, but when we talk about onion varieties, we mean whether they are “long-day,” “short-day,” or “day-neutral.”
- Bulbs form with 14+ hours of daylight
- Best for northern regions (for those in the U. S. If you draw a line from San Francisco, California, to Washington, D.C., this is the upper half of the country. C. ) .
- Best planted in late winter to early spring
- Typically good storage onions
- On average take 90-110 days to maturity
- Bulbs form with 10-12 hours of daylight
- Best to grow in zones 7 and above; bulbs won’t get as big if they are grown in colder areas.
- If you plant it in the fall, it will be ready in late spring.
- About 110 days to grow up in warmer areas if planted in the fall and 75 days in colder areas if planted in early spring.
- Bulbs form with 12-14 hours of daylight
- Ideal for zones 5-6
- Plant in late fall or early winter if you live in a mild climate or early spring if you live in a cold climate.
- Typically sweet varieties
- On average takes 110 days to maturity
I think you should quickly look up your area online to find out what kind of onion you should grow.
If you want to store an onion for a long time, make sure you pick a type that is known for being good at that.
We like to grow a lot of different kinds so that we can eat some right away, store others for a short time, and have enough to last us until next year’s harvest.
TIP: Freeze-dried onions are one of the best ways to save time in the kitchen if you have a freeze dryer. They’re easy to store and can be used in a lot of different way.
Time To Start Onions From Seed – Everything You Need To Know – Long Day Short Day – Sets vs Seeds
How long does it take for onion seeds to germinate?
Though it can vary depending on the environment, you can expect to see your onion seeds germinating sometime between 5-10 days after sowing them. If it’s too cold or wet, the process can be slowed. Keep the soil evenly moist but never soggy, and add bottom heat to help speed things up. What Do Onion Seedlings Look Like?
How do you grow onions from seeds?
Once your seeds have germinated, you’ll realize this because you’ll see little sprouts of life sticking up out of the soil. So you’ll need to be patient and allow the onions to grow. You will continue misting the soil as needed. Again, you don’t want to overwater, so check your soil daily.
How long does it take to grow onions?
The number of days it takes to grow onions from seed to harvest can vary widely between the different varieties. But on average, the time from sowing to maturity falls somewhere between 3-5 months. You can always enjoy some of your crop earlier however, they are edible at any size.
When should I plant onion seeds?
Onion seeds are usually started indoors approximately six weeks prior to the outdoor soil temperature being around 50 degrees Fahrenheit. If you’re starting with seedlings, plant them outside when the soil temperature is around 50 degrees Fahrenheit as well. It’s also possible to plant in the fall in warmer climates.