Onion Harvest Date Calculator: Estimate by Planting Date
By Ada Jones · Updated October 2026 · 6 min read
Short answer: estimate your harvest date by adding your variety’s “days to maturity” (printed on the seed packet or set label, typically 90-120 days) to your planting date, then watching the plants rather than the calendar for the actual trigger — tops falling over on their own. Use the table below to estimate by method, then confirm visually.
Estimate Your Harvest Date
| Growing Method | Typical Days to Maturity | Example: Planted April 1 |
|---|---|---|
| From seed (indoor start, then transplant) | 150-180 days from sowing (including 8-10 weeks indoors) | Harvest late August to late September |
| From sets (small bulbs) | 90-120 days from planting | Harvest late June to late July |
| From nursery transplants | 100-120 days from transplanting | Harvest mid-July to late July |
| Green onions / scallions (any method, harvested young) | 50-70 days | Harvest mid-to-late May |
These ranges assume typical growing conditions for your variety’s day-length category. Cooler-than-average seasons extend the timeline; a long hot stretch early in the season can shorten it, sometimes by triggering early bolting.
Why the Calendar Is Only a Starting Estimate
Onion bulbing is triggered primarily by day length reaching your variety’s threshold, not by a fixed number of days. That means two gardeners who planted the exact same variety on the exact same date, but at different latitudes, can see noticeably different harvest dates because the days lengthen at different rates depending on how far they are from the equator. Use the days-to-maturity number to get in the right range, then switch to watching the plants — tops falling over, necks softening — as harvest approaches.
FAQ
Can I harvest onions early if I need the space?
Yes — immature onions (“spring onions” at that stage) are edible, just smaller and won’t store as long. They won’t have fully developed their papery storage skin.
What if my onions still haven’t matured well past the expected date?
Check whether you planted the right day-length type for your latitude and whether they got enough nitrogen early in the season — see our guide on bulbs not forming for the full troubleshooting list.
Final Thoughts
Use the days-to-maturity estimate to plan your season, but trust the plant’s own signals for the actual harvest call. Once you’re close, see our full harvest, curing, and storage guide for what to do next.
How This Guide Was Checked
Based on seed packet days-to-maturity data across major seed suppliers and day-length/latitude bulbing research. Need help estimating your own date? Contact us.
Related Onion-Growing Guides
- How to Harvest, Cure, and Store Onions for Months
- How Long Does It Take to Grow Onions? A Timeline by Method
- When to Plant Onions by Zone (Plus Companion Planting)
See the full How to Grow Onions guide for the complete seed-to-harvest walkthrough.
