Onions: Spacing, Yield & Planting Dates
Plant count & yield calculator
Pre-filled for this crop — adjust bed size or pick a different vegetable.
Enter bed size to count plants.
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Seed starting dates
Pre-filled last frost — change the date to rebuild the full crop schedule. For Onions with this frost date : start indoors ~Feb 4, transplant ~Mar 18 .
Pick a last frost date for the schedule.
Your result
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Show the math & assumptions
Assumptions and formulas will appear here once you calculate.
About onions
Onions are a kitchen staple worth growing at home for the range of sweet, storage, and specialty varieties unavailable in most stores.
Spacing & yield
Onions wants 4×12 inches and about 0.3 lb per plant at ~100 days to maturity.
Growing tips
- Start seeds indoors 10 weeks before last frost — onions need a long runway.
- Choose short-day types in the South and long-day types in the North for proper bulbing.
- Stop watering once tops begin falling over naturally to cure bulbs in the ground.
- Trim transplant tops to 5 inches at planting to reduce transplant stress.
Common mistakes
- Selecting the wrong day-length variety for your latitude, resulting in no bulb formation.
- Planting too deep — set transplants just 1 inch deep so the bulb can expand at the surface.
- Storing uncured onions, which rot within weeks.
Harvest & storage
Lift bulbs when most tops have fallen over and necks are soft, about 100 days from transplant.
Cure in a warm, airy spot for 2-3 weeks, then store in mesh bags at 35-50 F for months.
Companion planting
Good neighbors for onions: carrots, lettuce, beets, strawberries, chamomile. Avoid planting beside: beans, peas, asparagus.
Planting calendar
Start indoors about 10 weeks before last frost, then transplant 4 weeks before frost. Use the seed-starting calculator above with your real county frost date — the April 15 default is only a worked example (zone 6 style).
Estimates only — consult your local extension office for advice specific to your land and animals.
Frequently asked questions
- When should I start onion seeds?
- Start seeds indoors 10 weeks before your last frost date; transplant outdoors 4 weeks before last frost.
- How far apart do onions go?
- Space 4 inches apart in rows 12 inches apart for standard-size bulbs.
- How big will one onion get?
- Each plant produces a single bulb averaging about 0.3 lb under home garden conditions.