Timing Guide
How Long Does It Take to Grow Onions? A Timeline by Method
Bulb onions take roughly 3 to 5 months from planting to harvest, depending on how you start them: up to 5 months from seed, 2 to 4 months from transplants, and about 2 months from sets — the fastest of the three. Green onions are much quicker, ready in about 50 to 70 days. The number that matters most isn’t a date on a calendar, though; it’s the tops falling over, which is how you know bulbs are actually done.
Time to Harvest by Starting Method
| Method | Time to Harvest | Notes |
|---|---|---|
| Seed | Up to 5 months | Start indoors 8 to 12 weeks before your last frost |
| Transplants | 2 to 4 months | Already a head start on growth when you plant them out |
| Sets | About 2 months | The fastest route, but limited variety choice |
| Green onions (any method) | 50 to 70 days | Pulled young, before the bulb fully forms |
| An onion you already have | Greens in 1 to 2 weeks; bulbs unreliable | Not a dependable storage crop |
Why Do Sources Disagree on Onion Growing Time?
Search around and you’ll find onions quoted at anywhere from 90 days to 5 months, and the ranges aren’t actually contradicting each other once you know what each one is measuring. A number like “95 to 115 days” usually describes transplants, already weeks old when planted out. “Up to 5 months” almost always means counting from the day you sowed seed, including the slow indoor-growing stage. And “about 2 months” is sets, which skip the slowest early stages entirely because the set itself is already a small, year-old onion. The method you start with changes the clock more than anything else.
How to Tell Your Onions Are Actually Ready
Forget the calendar once your onions are close. The real sign is the tops: harvest when about half to most of the leaves have fallen over and started to dry on their own. Illinois Extension warns that breaking the tops over early to speed things up actually backfires — it interrupts growth and gives smaller bulbs that keep less well in storage. If autumn rains are close, don’t wait through them either; mature onions left in cool, wet soil rot quickly.
- Too early: tops still upright and green — leave them, the bulb is still sizing up.
- Right on time: about half the tops have flopped over and begun to dry.
- Running late: most tops down and dry, necks soft — harvest now, before rain or rot sets in.
What Slows Onions Down
A few things can stretch the timeline well past the ranges above: planting the wrong day-length type for your latitude (it may never bulb, no matter how long you wait), a late start, crowding, too little sun, or a cold snap after planting that pushes the plant to bolt instead of bulb. If your onions are taking much longer than these ranges and the tops never flop, something upstream is off, not just the clock. See our main growing guide for the full troubleshooting breakdown.
Frequently Asked Questions
How long does it take for onions to grow from seed?
Up to 5 months total, counting from indoor sowing through to harvest.
How long does it take onions to grow from sets?
About 2 months, the fastest of the common starting methods.
How long for green onions to grow?
About 50 to 70 days from planting, whether started from seed or sets.
How do I know exactly when to harvest, rather than guessing by days?
Watch the tops, not the calendar. Harvest once about half to most of them have fallen over and begun to dry on their own.
Final Thoughts
There’s no single answer to “how long do onions take to grow” because the method you start with changes everything — sets in two months, transplants in a season, seed in up to five. Learn the tops-falling-over sign and you’ll never need to guess by the calendar again. For a full breakdown of each method, see growing from seed, growing from sets, or the main growing guide.
How This Guide Was Checked
Related Onion-Growing Guides
- Growing Onions From Seed: The Complete Step-by-Step Method
- Growing Onions From Sets: The Fastest Way From Garden to Harvest
- Onion Sets vs Transplants vs Seeds: Which Should You Choose?
- When to Plant Onions by Zone (Plus Companion Planting)
See the full How to Grow Onions guide for the complete seed-to-harvest walkthrough.
