When you grow onions from seeds, you can choose from more varieties than when you buy them as sets or transplants. With seeds, you can pick from more than 125 different kinds of onions that will grow well in your area and meet your cooking needs. Onions grown from seeds, on the other hand, need more time to fully grow, so be patient.
From planting the seeds to harvesting the onions, this complete guide will show you the whole process. You’ll learn:
- The different stages of onion growth and how long each phase takes
- Factors that affect onion growth rate
- When to start seeds indoors vs direct sowing
- Average days to maturity for common onion types
- Tips for speeding up growth
Knowing the stages and timing of onion growth will help you get a healthy, plentiful harvest. So let’s dive in!.
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 base signals bulb growth. Takes 6-10 weeks.
- Bulb Maturity – Onions plump up. Takes 2-4 weeks.
- Foliage Dieback – Leaves yellow and fall when bulbs ripe. Takes 1-2 weeks.
- Curing – Harvested bulbs dried for storage. Takes 2+ weeks.
Total time from seed to harvest is 13-22 weeks depending on variety. Then curing adds more time before onions are ready to eat or store. Proper curing is crucial for long term storage.
What Affects Onion Growth Speed?
Several variables determine the rate onions move through each phase:
- Onion Type – Short-day varieties grow fastest. Long-day onions take longer.
- Climate – Warm climates with long growing seasons accelerate 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 enhances growth.
- Proper Care – Watering, fertilizing, 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 provides more control but requires 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 adequate time to mature before transplanting outside.
Use a seed starting mix in containers at least 2 inches deep. Cover seeds lightly, about 1⁄4 inch deep. Grow lights will accelerate growth. Transplant outdoors when seedlings are pencil-thick.
Direct Sowing Outdoors
Plant seeds directly in the garden four to six weeks before the date of your last spring frost. This works well for short-day varieties in warm places.
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 sprouted.
Direct sowing avoids transplant shock but allows less control over growing conditions.
Onion Seed to Harvest Timeline
Here’s a breakdown of approximately how long popular onion varieties need from seed sowing to maturity:
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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, ideal for southern gardeners. Examples: ‘Texas Early White’, ‘Southern Belle’, ‘Grano’.
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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. Recommended for northern regions. Examples: ‘Copra’, ‘Wethersfield’, ‘Patterson’.
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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’.
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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’.
Tips for Boosting Onion Growth Rate
Here are some tips to help your onions reach maturity as quickly as possible:
- Select short or intermediate-day varieties suited to your climate.
- Start seeds indoors to give plants a head start on growth.
- Transplant into warm, loose soil enriched with compost or manure.
- Water consistently to keep soil evenly moist but not soggy.
- Fertilize every 2-3 weeks with a balanced organic fertilizer.
- Mulch to retain moisture and reduce weeds.
- Control pests like onion maggots that slow development.
- 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!
Frequently Asked Questions
How long do onions take to grow?
From planting to harvest, onions typically take 90-120 days to reach full maturity. This duration varies by onion variety, climate, and growing conditions.
How do you know when onions are ready to dig up?
Harvest onions when their tops turn yellow and fall over, signaling maturity. Also check bulb size by gently digging around the base to ensure they’ve reached a good size for the variety. The bulbs should be firm and well-formed.
How many onions do you get from one plant?
You can typically harvest one large, mature onion bulb from each plant. However, some multiplier onion varieties yield several smaller onions per plant in a cluster.
Do onion sets multiply?
Yes, onion sets can multiply. When planted, a set develops one bulb the first year. But some varieties also generate small “set” bulbs around the base that can be replanted the next year for greater yield.
Conclusion
How to grow onions
You can grow onions from seed, but it’s much easier and quicker to grow them from sets (small onions). Most are heat-treated, meaning they’re less likely to bolt (produce flowers), which stops the onions bulking up. One small onion set grows into one larger onion. Plant these in autumn or spring, 10-15cm apart in well-prepared, moisture-retentive, fertile soil in full sun. Keep the area weed free and water in dry periods. Harvest the onions when they’re big enough to eat or the foliage has turned brown and started to wither.
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.
The biggest piece of advice she has to offer is to find varieties that grow well in your climate (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.
When it comes to onion seeds, however, Melissa has found that the expiration dates hold more true and recommends if you’re planting onions using older seeds to double or triple the amount you plant, just in case your germination rate is low.
When it comes to growing onions, many people just think of yellow, purple, or sweet onions. And although these are types of onions, what we mean when growing onion varieties is whether they’re “long-day”, “short-day”, or “day-neutral” varieties.
- 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 multiple varieties, some for fresh eating, some for short-term storage, and some to get us all the way through the spring until next year’s harvest.
TIP: If you happen to have a freeze dryer, we’ve found freeze-dried onions are one of the best time-savers in the kitchen! They’re easy to preserve and can be used in so many dishes.