How Far Apart to Plant Onions

Onion spacing is really a question about bulb size. The closer you plant them, the smaller each bulb stays. The wider you plant them, the bigger they get.

That is the whole trade-off, and it is why the charts seem to disagree. Some say 2 inches, some say 6. Both are right for different goals.

Spacing in rows vs a raised bed or square-foot garden

The right number depends on how you garden. In-ground rows and square-foot beds are two different layouts.

For traditional rows, space onions about 5 inches apart in rows 12 inches apart. That 5-inch gap sits inside the 4 to 6 inch range North Dakota State and Illinois Extension recommend for large bulbs. The row spacing gives you a path to weed and lets air move through.

For a raised bed or square-foot garden, you skip rows and plant on a grid. The square-foot-gardening standard is 9 onions per square foot, which is a 3-by-3 layout on a 4-inch grid. Onions are upright and narrow, so they pack tight without shading each other out.

Onions are also light feeders that hate weed competition. If you are filling a new bed, our guide to the plant spacing chart sets the grid for every crop before you plant a single set.

Onion spacing by method, at a glance

Pick your goal first, then read the spacing across. These ranges come from Illinois, North Dakota State, Cornell, and Oregon State Extension guidance.

The pattern is simple. More space per plant means more bulb. Less space means more onions, but smaller ones.

A worked example: how many onions fit a 4x8 bed

A 4x8 bed is 32 square feet. At the square-foot rate of 9 onions per square foot, that is 288 onions on a 4-inch grid (32 × 9).

That number assumes you want a wall of medium bulbs. If you want bigger onions, drop to a 6-inch grid at 4 per square foot, which gives about 128 onions with real room to swell.

The math is the same either way: square feet times plants per square foot. The grid you pick decides the bulb size.

Square vs triangular layout

How you arrange the onions, not just how far apart, changes how many fit. A triangular (offset) grid packs in roughly 15% more plants than a straight square grid over a large bed.

In a square grid, every onion lines up in neat rows and columns. In a triangular grid, each row shifts over by half a space, so plants nestle into the gaps of the row beside them. That offset is what buys the extra density.

The catch is bed size. In a small bed the edges eat the gain, so the 15% only shows up once the bed is big enough for the pattern to repeat.

square grid (5in)        triangular grid (5in)
●  ●  ●  ●  ●            ●  ●  ●  ●  ●
●  ●  ●  ●  ●              ●  ●  ●  ●
= more uniform           = ~15% denser at scale

Run your own bed size through the Plant Spacing Calculator and it counts both layouts so you can see which wins for your exact dimensions.

Why spacing matters for onions

Spacing decides two things for onions: how big the bulbs get, and how often the crop gets sick. Both come down to giving each plant room.

On bulb size, the extension guidance is consistent. Utah State and Illinois Extension both note that crowded onions stay small because they compete for light, water, and nutrients. Space them 4 to 5 inches apart and each one has the resources to size up.

On disease, airflow is the lever. Crowded onions trap humid air and dry slowly, and damp foliage is where trouble starts. Utah State, Cornell, and Minnesota Extension tie poor spacing to downy mildew, neck rot, and pink root. Give plants room and they dry fast, which starves the fungus.

Common spacing mistakes

A few errors show up again and again in onion beds. Each one is easy to avoid once you know the number.

• Planting for bulbs but spacing for scallions (under 3 inches).
• Forgetting that onions need weeding room, so the rows crowd shut.
• Counting raised-bed squares at 16 per square foot, a rate meant for scallions, not bulbs.
• Setting bulbs too deep, which slows sizing as much as crowding does.

The fix for all four is the same. Decide your goal first, bulbs or scallions, then space for the full-grown plant and give air a path between every onion.

The whole job is one decision and one measurement. For full bulbs, space at 5 inches as your default, wider if you want them big. Get the air moving between plants and you have done the single biggest thing for a healthy crop. From there, when to harvest onions picks up the season.

Got your bed size? Open the Plant Spacing Calculator and see exactly how many onions fit, square or triangular.