When to Plant Onions
Onions are a hardy cool-season vegetable. They can take a hard frost.
Start seeds indoors 10 to 12 weeks before the last spring frost, and plant out 1 to 4 weeks before the last frost. The first harvest comes about 90 to 120 days after transplanting.
Example dates
The same rules in dates for three climates, using typical frost dates. Enter your ZIP code above for the dates where you live.
| Task | Last frost Mar 15first Nov 15 | Last frost Apr 15first Oct 25 | Last frost May 15first Sep 30 |
|---|---|---|---|
| Start seeds indoors | Dec 21 – Jan 4 | Jan 21 – Feb 4 | Feb 20 – Mar 6 |
| Harden off | Feb 8 – 14 | Mar 11 – 17 | Apr 10 – 16 |
| Plant out | Feb 15 – Mar 8 | Mar 18 – Apr 8 | Apr 17 – May 8 |
| Harvest | May 16 – 30 | Jun 16 – 30 | Jul 16 – 30 |
Growing onions
Plant sets or transplants early, keep them weeded, and harvest when most tops have fallen over.
- Spacing: 4 in apart, in rows 12 in apart. In a raised bed, 9 per sq ft at square-foot spacing.
- Days to harvest: 90 to 120 from transplanting, then about 2 weeks of picking.
- Rotation: onions are in the onion family. Plant them where nothing from that family grew in the last two years. See crop rotation.
- Traditional companions: beet, bell pepper, broccoli, brussels sprouts, cabbage, carrot, cauliflower, celery, chamomile (german), cherry tomato, collards, dill, head lettuce, hot pepper, kale, kohlrabi, leaf lettuce, romaine lettuce, salad mix (baby greens), spinach, strawberry, swiss chard, tomato. See companion plants for onions.
- Usually kept apart from: bush bean, pea (shelling/snap/snow), pole bean.
Plan your beds with these dates
Draw your beds, tap squares to plant onions and everything else, and get every crop's dates for your ZIP code in one calendar. Free, in your browser.
Open the garden plannerQuestions
When do I start onions indoors?
10 to 12 weeks before the last spring frost: with a last frost of April 15, that's Jan 21 – Feb 4. Enter your ZIP code above for your own dates.
Can onions go in before the last frost?
Yes. Onions are hardy: plant them out 1 to 4 weeks before the last spring frost.
How long do onions take to grow?
About 90 to 120 days from transplanting to the first harvest, which then lasts about 2 weeks. Varieties differ: check the seed packet.
More planting dates
Sources
- NOAA National Centers for Environmental Information, U.S. Climate Normals 1991–2020 (annual/seasonal, by station: freeze dates at 32 °F)
- Colorado State University Extension: Vegetable Planting Guide (CMG GardenNotes #720)
- Virginia Cooperative Extension, Virginia Tech: Virginia's Home Garden Vegetable Planting Guide: Recommended Planting Dates and Amounts to Plant (426-331 / SPES-673P, 2025)
- University of Maryland Extension: Vegetable Planting Calendar for central Maryland
- UNH Cooperative Extension: Growing Vegetables: When to Plant your Vegetable Garden (2016)
- NC State Extension: Extension Gardener Handbook, Chapter 16: Vegetable Gardening
- WSU Extension: Pacific Northwest Gardener's Handbook, Chapter 7: Vegetable Gardening
- Iowa State University Extension and Outreach: Vegetable Planting and Harvesting Times (chart, central Iowa)
- Iowa State: Germination Requirements for Annuals and Vegetables
- Iowa State: All About Onions
- Utah State University Extension: Suggested Vegetable Planting Dates for Utah
- Cornell Cooperative Extension, Rockland County: Vegetable Planting Guide (Hort 52)
- Clemson Cooperative Extension HGIC: Small-Scale Gardening (square-foot planting guide)
- UC Master Gardener Program, UC ANR: Companion Planting Chart: Companion Planting for Edible Crops
- University of Wisconsin–Madison Extension, Kenosha County: Companion Plants for the Vegetable Garden (column, 2012)
- Oregon State University Extension Service: Herbs and Flowers in the Vegetable Garden
- Utah State University Extension, Utah 4-H: Creating Sustainable School and Home Gardens: Companion Planting (2025)
- SDSU Extension: Square-Foot Garden Sample Planting Layout (P-00379, 2026)
- University of Arizona Cooperative Extension, Yavapai County: The Art of Companion Planting (Master Gardener presentation, 2023)
- Clemson Cooperative Extension HGIC: Plant Partners: 5 Benefits of Companion Planting (2025)
- N.C. A&T State University Cooperative Extension: Five Veggies You Can Grow at Home