Onion Spacing Guide: How Many Per Square Foot
By Kevin Parker · Updated October 2026 · 6 min read
Onion spacing for full-size bulbs is four to six inches. Keep rows twelve to eighteen inches apart as well. Grid planting fits four to nine per square foot.
Onion Spacing by Goal
Counts below use grid planting, where every plant gets an equal square of soil.
| Goal | Spacing | Plants per square foot (grid) |
|---|---|---|
| Maximum bulb size | 6 inches apart | 4 |
| Standard full-size bulbs | 4 inches apart | 9 |
| Medium bulbs in rich soil | 5 inches apart | About 6 |
| Thin for green onions, let the rest bulb | 3 inches apart, thin every other plant at 6–8 weeks | 16 planted, about 8 after thinning |
| Green onions only | 1–2 inches apart | 36 at 2 inches, more at 1 inch |
How to Mark Out Onion Spacing, Step by Step
Even spacing is much easier with a marked grid. String lines or a marked board both work well. Five minutes of marking saves weeks of crowding problems.
- Divide each bed side into equal measured sections first.
- Press shallow lines across the soil with a board.
- Cross those lines to form a grid of squares.
- Poke one planting hole at each square’s centre point.
- Drop one set or seedling into every hole.
The grid keeps every gap equal without constant measuring. Equal gaps mean equal light, water and food. It is the first decision in the planting plan our how to grow onions guide walks through.
Why Crowding Hurts Bulb Size
Onions compete directly for light, water, and nutrients when crowded, and since bulb size is largely set by how much leaf growth happens before bulbing starts, crowded plants simply can’t build as many leaves (and therefore rings) as properly spaced ones. Thinning is a useful middle ground — plant closer than final spacing, then pull every other plant as a green onion once they’re a few inches tall, leaving the rest at full spacing to bulb normally.
FAQ
How close can I plant onions in a raised bed?
The same 4-6 inch spacing applies in raised beds — the bed itself doesn’t change the plant’s need for room to bulb, though raised beds do make tighter, more even grid spacing easier to achieve.
Do bigger varieties need wider spacing?
Yes — varieties bred for very large bulbs benefit from the wider end of the range (6+ inches) to avoid any competition capping their size potential.
How many onions can I plant per square foot?
Nine standard bulbs fit at four inch spacing. Six inch spacing fits four larger bulbs instead. Three inch spacing fits sixteen before any thinning.
How far apart should rows of onions be?
Keep rows twelve to eighteen inches apart in beds. Wider rows leave room for hoeing and harvesting. In-row spacing still decides the final bulb size.
Can I plant onions close and thin them later?
Yes, and thinning is a smart two-harvest trick. Plant at three inches and pull every other plant. Eat the thinnings young as green onions in spring.
What happens if onions are planted too close?
Crowded onions fight for light, water and nutrients. They grow fewer leaves before bulbing starts each season. Fewer leaves mean fewer rings and smaller bulbs.
How far apart do green onions go?
Green onions grow happily one to two inches apart. They are pulled young, long before bulbs swell. Thirty-six or more fit inside one square foot.
Final Thoughts
Spacing is one of the easiest variables to get right, and one of the most impactful. See our bulb size guide for the other factors that matter alongside spacing.
How This Guide Was Checked
The spacings here match Iowa State University Extension guidance. Fine Gardening’s planting guidance was checked against them too. Every per-square-foot count was worked out from the spacing itself. Counts from sites that mixed measuring methods were left out.
Written by Kevin Parker · grows onions in his own beds in California. Figures are checked against university extension and grower sources, linked on each page. More about Kevin.
