Growing onions from seed is one of the most satisfying projects you can take on in a backyard garden. It’s slower than planting sets, but starting from seed gives you access to a wider variety of onions and allows you to control every stage of the process. In this article, I’ll walk you through how long does onion take to grow from seed, what factors influence its growth rate, and how you can ensure a healthy, abundant harvest.
Understanding How Long Onions Take to Grow from Seed
If you’ve ever asked, “how long does onion take to grow from seed?”, the answer is: it depends on the variety and your growing conditions. On average, onions take 100 to 160 days to mature from seed. That’s roughly 3 to 5 months from the time you sow the seed to the time you harvest fully formed bulbs.
As a backyard gardener, I usually start my onion seeds indoors about 10 to 12 weeks before the last spring frost. This gives the seedlings time to get strong before I transplant them outdoors. Once they’re in the ground, I wait patiently—watering, weeding, and watching as they slowly grow into one of my favorite vegetables to harvest.
Here’s a quick breakdown of the growth timeline:
- Germination: 7–14 days
- Seedling development: 4–6 weeks
- Bulbing: Starts after 60–90 days
- Full maturity: Around 100–160 days
The timeline can vary, but with consistent care and planning, you can enjoy a reliable onion harvest from seed every season.
What Affects How Long Onions Take to Grow?
Many gardeners underestimate the role that location, climate, and variety play in onion growth. If you’re wondering how long does onion take to grow from seed, consider these key influences:
1. Day Length
Onions are photoperiodic, meaning they depend on day length to initiate bulbing. That’s why understanding your region’s day length is crucial. There are three types:
- Short-day onions: Bulb at 10–12 hours of daylight. Great for southern states.
- Long-day onions: Need 14–16 hours. Best for northern climates.
- Intermediate-day onions: Do well in the middle of the U.S.
I live in a transitional zone, so I’ve had good luck with intermediate-day types like ‘Candy’ and ‘Red Burgundy.’ Choosing the right type ensures your onions start bulbing at the right time, preventing stunted growth or bolting.
2. Temperature and Soil Conditions
Onion seeds germinate best in 50°F to 75°F soil. Cool weather promotes root development, while overly warm conditions can stress young plants.
My best results have come from planting in raised beds with loose, well-drained soil rich in compost. The seedlings thrive in early spring temperatures and gradually adapt as the season warms up.
3. Onion Variety
Some varieties naturally grow faster than others. For example:
- ‘White Lisbon’: Ready in 110 days
- ‘Walla Walla’: Takes 125–130 days
- ‘Texas Early Grano’: Matures in about 100–110 days
Check your seed packet for the expected days to maturity. This simple step can help answer how long does onion take to grow from seed for your specific variety.
How to Start Onions from Seed
Starting from seed might seem like extra work, but it’s more affordable and offers more variety. Here’s how I do it every year in my backyard:
1. Indoor Seeding
I sow seeds in seed-starting trays filled with moist, well-draining mix about 10–12 weeks before the last frost. I aim for early January to February, depending on the year. Plant the seeds about ¼ inch deep and keep the tray in a warm (around 70°F) location.
Within 7–10 days, the seeds sprout. That’s when I place them under grow lights for about 14 hours a day to keep them strong and compact.
2. Transplanting Outdoors
Once seedlings are the size of a pencil (usually after 8–10 weeks), I start hardening them off by placing them outside during the day for a week. Then I transplant them into well-prepared soil in full sun.
I space them about 4 inches apart in rows 12 inches apart. Good spacing ensures healthy bulb formation.
This approach shaves weeks off the outdoor growth period, effectively shortening the answer to how long does onion take to grow from seed.
Growing Onions: Weekly Care and Maintenance
Caring for onions isn’t overly complex, but consistency is key if you want them to mature on time.
Watering
Onions like consistent moisture, especially in early stages and during bulb formation. I water them about once a week with 1 inch of water. Too much moisture can lead to rot, so well-draining soil is crucial.
Fertilization
During the first 60 days, I fertilize every 2–3 weeks with a nitrogen-rich organic fertilizer like fish emulsion. Once bulbing begins, I switch to a low-nitrogen, higher phosphorus and potassium blend.
Mulching and Weeding
Onions don’t compete well with weeds. I use a light mulch layer of straw or grass clippings to suppress weeds and retain moisture. Regular hand-weeding is part of my routine.
These weekly tasks keep your onions on track so they mature within that 100–160 day window. In other words, they help control how long does onion take to grow from seed in your specific garden.
When and How to Harvest Onions
After several months of patient care, the day finally comes—onions are ready for harvest! You’ll know it’s time when the tops start to yellow and fall over.
I usually let them sit in the ground for another 7–10 days after that, which helps the outer layers dry slightly. Then I pull them up on a dry day and lay them in a shaded area to cure for 2–3 weeks.
This curing process is crucial for storage. A well-cured onion can last for months in a cool, dry place.
Common Mistakes That Delay Onion Growth
If your onions seem stuck in seedling mode or not bulbing, you’re not alone. I’ve made these mistakes myself, and they definitely impact how long does onion take to grow from seed:
- Wrong variety for your location
- Inadequate sunlight (less than 6 hours/day)
- Compacted or poor-draining soil
- Overcrowding or poor thinning
- Inconsistent watering or nutrient deficiencies
Learning from these mistakes has helped me consistently grow full, healthy onions right on time.
Frequently Asked Questions
Which is the best month to plant onions?
The best month to plant onions depends on your region, but generally, plant seeds indoors in January or February and transplant in March or April. In warmer climates, onions can be planted directly in late fall for a spring harvest.
What is the fastest way to grow onions?
The fastest way to grow onions is by planting onion sets instead of seeds. Sets are small, pre-grown bulbs that skip the germination phase and mature in 60 to 80 days, significantly reducing the time compared to starting from seed.
How many onion seeds per cell?
Sow 3 to 5 onion seeds per cell when starting indoors. Once the seedlings sprout and grow a few inches tall, thin them down to the strongest 2 or 3 per cell to ensure healthy development without overcrowding.
How long does it take to regrow onions?
Regrowing onions from kitchen scraps, like the root base, takes about 3 to 4 weeks to produce green tops and 90 to 120 days to regrow a full bulb. However, full regrowth isn’t always guaranteed depending on conditions and variety.
How many onions do you get from one plant?
Each onion plant produces one bulb. However, you can also harvest the green tops as scallions if picked early. For continuous yield, stagger your planting or grow multiple plants throughout the season for a steady onion supply.
Final Thoughts: Patience Is Part of the Process
So, how long does onion take to grow from seed? Plan for anywhere between 100 to 160 days, and tailor your approach to your climate, soil, and preferred variety. With a little patience and care, you can grow robust, flavorful onions right in your backyard—even starting from humble little seeds.
Every year I grow onions, I’m reminded that gardening is a journey. The long wait from seed to harvest is part of what makes it so rewarding. Trust the process, learn from each season, and you’ll enjoy homegrown onions that store well and taste better than anything from the store.
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References
- University of Minnesota Extension. Growing onions in home gardens
- Texas A&M AgriLife Extension. Onion Production
- Cornell University Vegetable Growing Guides. Onions
- University of Illinois Extension. Onions
