Last Updated on September 13, 2026
How Many Onions per Square Foot?
4 bulb onions per square foot for full-size storage onions. If you are growing green onions or bunching onions, that number jumps to 16 per square foot, and they get their own page.
The spacing pattern
| Square foot method | 4 per square: a 2 x 2 grid, each onion about 6 inches from its neighbors |
|---|---|
| Per square foot | 4 |
| 4 x 4 bed (16 squares) | 64 onions |
| 4 x 8 bed (32 squares) | 128 onions |
Onions size up by leaf count, not by crowding, but every bulb still needs about 6 inches of soil around it to swell. Closer than 4 per square and you get more onions that are all smaller; that is fine on purpose for boilers or pearl onions, not for storage onions.
Planting the square
- Mark the square into a 2 x 2 grid.
- Set one transplant or seedling at each of the 4 points, roots just covered; from seed, sow a pinch at each point about a quarter inch deep and thin to one.
- Keep the soil evenly moist; onions stop bulbing when they dry out.
Tim’s growing notes
I start onions from seed indoors in January and transplant, and I trim the tops while they grow. The full method is in How to Grow Large Onions.
Soil temperature for germination
From my Seed Germination Temperature Chart: onions germinate from 32°F, do best at 65-85°F, and stop above 95°F.
Days for seedlings to emerge at different soil temperatures, from the same chart:
| Soil temperature | Days to emerge |
|---|---|
| 50°F | 13 days |
| 59°F | 7 days |
| 68°F | 5 days |
| 77°F | 4 days |
When to plant onions
These are the windows the Plan My Garden planner uses, counted from your average last spring frost. Enter your frost date on the seed starting calendar to turn them into dates. Onions are the earliest seed I start every year.
| Start indoors | 12 weeks before to 11 weeks before your last frost |
|---|---|
| Transplant out | 4 weeks before to 2 weeks before your last frost |
| Days to maturity | about 100 days |
How I grow them, in brief
Onions bulb by day length, so the first job is the right type for your latitude: long-day varieties in the north, short-day in the south. I start seed indoors 10 to 12 weeks before the last frost, in a warm spot since they germinate best at 65 to 85°F, and trim the tops to about four inches while they grow so the seedlings thicken instead of flopping. They go out into a sunny bed with good drainage a few weeks before the last frost, and they need steady water right through bulbing. When the tops yellow and fall over in late summer they are done: pull them, cure them somewhere airy for a couple of weeks, and store the ones with tight necks. All of it, with photos, is in How to Grow Large Onions.
Where I get seed
I buy onion seed and onion plants from Wood Prairie in Maine. Their organic onion seed includes Ailsa Craig, Valencia and Gladstone, and if you want a head start, their organic onion plants ship ready to set out. Code PMG5 takes 5 percent off.
Quick questions
Can I plant onions closer than 4 per square?
Yes, at 9 or 16 per square you get more but smaller onions. That is the right choice for green onions or pearl onions, not for storage bulbs.
Seed, sets or plants?
I grow from seed started indoors in January, and buy plants when I run out of time. Sets are the easiest but give the fewest choices of variety.
Let the planner place them
Plan My Garden is free to start: draw your beds, pick onions and everything else you want to grow, and it places each plant at the right spacing and gives you a planting schedule for your zip code.
Related: Square Foot Gardening Chart · Seed Germination Temperature Chart · Spring Onion vs Green Onion
