How Far Apart to Plant Onions in a Raised Bed

Plant onions 4 inches apart for moderate-size bulbs, 2 inches apart for green onions, and 8 inches apart for large bulbs; use a 4-inch by 4-inch grid for moderate bulbs in a block-planted raised bed. The right spacing depends on whether you want scallions, everyday cooking onions, or the largest bulbs your variety can produce. Your starting material, seed, sets, or transplants, also changes how you plant and thin the bed.

Use this chart to choose your final spacing before you mark the bed.

Harvest Goal or Layout	Final Plant Spacing	Best Raised-Bed Approach
Green onions or scallions	2 inches apart	Grow in a band or close row and harvest young
Moderate-size bulbs	4 inches apart	Use rows or a 4-inch by 4-inch block grid
Large bulbs	8 inches apart	Use wider conventional rows
Conventional row layout	1–8 inches between plants; 12–24 inches between rows	Match the in-row space to the bulb size you want

What Determines Onion Spacing

Onion spacing is a harvest decision first and a layout decision second.

An onion grown for a green top or small scallion does not need the same room as an onion expected to make a full-size bulb. Wider spacing gives each plant more access to light, water, and soil nutrients, which supports larger bulbs. Closer spacing lets you grow more plants, but the harvest will be younger or smaller.

The onion’s color does not determine spacing. Red, yellow, and white onions all need room based on the size you want to harvest.

Your planting material matters, too:

Seeds are usually sown more closely than their final spacing, then thinned.
Sets are small, dormant onion bulbs. They can begin close together and be thinned as they grow.
Transplants are young onion plants with roots and leaves already formed. They are usually placed directly at their final spacing.

Raised beds make all of this easier because you can create straight rows, wide bands, or square blocks.

How to Space Onions in a Raised Bed

Space onions 2 inches apart for green-onion harvest, 4 inches for moderate-size bulbs, and 8 inches for large bulbs.

Step 1: Prepare the Bed and Choose the Planting Site

Choose a raised bed with at least 6 to 8 hours of direct sunlight each day. Bulb onions need steady light to make good-sized bulbs.
Loosen the soil deeply enough for roots to spread and remove stones, old roots, and perennial weeds. Raised-bed soil should drain well but still hold moisture evenly.
Aim for a soil pH of 6.0 to 6.8 before planting. A soil test is the practical way to determine whether the bed is already in that range.
Plant in spring when the soil reaches 50°F. Onions tolerate cool conditions, but cold, wet soil can slow establishment.
Plan rows or blocks before planting so you can reach every part of the bed without stepping on the soil.

Step 2: Choose the Final Spacing for Your Harvest Goal

Thin onions grown for green-onion harvest to 2 inches apart. Harvest them young, before they need room to enlarge into bulbs.
Thin onions intended for moderate-size bulbs to 4 inches apart. This is a productive choice for most raised beds because it balances bulb size with the number of plants you can grow.
Thin onions intended for large bulbs to 8 inches apart. Use this wider space only when large bulbs are the goal and the variety is suited to your day length and growing season.
Use the seed packet, transplant tag, or variety description to confirm the exact spacing for a named cultivar. Some varieties are bred for smaller bulbs, bunching harvests, or unusually large storage onions.

Do not keep every seedling simply because it sprouted. Thinning is part of growing bulb onions, not a mistake or a waste. The thinnings can be used as green onions.

Step 3: Mark Rows or a Block Layout

Use conventional rows if you want clear paths for weeding and easy access. In a conventional layout, space plants 1 to 8 inches apart within rows and space rows 12 to 24 inches apart, depending on the final bulb size and your chosen layout. University of Maryland Extension includes this wide range for home-garden onions.
Use a block layout when you want to fit moderate-size onions efficiently into a raised bed. Mark planting positions in an even grid, with the same distance in every direction.
Keep rows or bands narrow enough to reach the center from either side of the bed. That lets you pull weeds and thin seedlings without stepping into the growing area and compacting the soil.
Leave a clear working strip between onion sections if the bed also holds another crop. Onion leaves are upright, but the plants still need open soil around their bulbs and room for your hands.

Step 4: Plant Seeds, Sets, or Transplants at the Right Depth

For onion seeds: sow in a straight line or marked block, cover lightly, and keep the seedbed evenly moist until seedlings emerge. Once the seedlings are established, thin them according to the bulb size you want.
For onion sets: place each set with the pointed end up. Start sets 2 to 3 inches apart, cover each with 1 inch of soil, and use variety directions if they call for a planting depth of 1 to 2 inches. Thin sets intended for bulb growth to the final spacing that matches the bulb size you want: 4 inches for moderate-size bulbs and 8 inches for large bulbs.
For onion transplants: make a hole deep enough to cover the roots without burying the neck where the leaves emerge. Set the transplant about 1 inch deep and firm soil gently around the roots.
Some commercially supplied onion transplants are planted 6 inches apart in rows 12 inches apart. Use that spacing only when it is specified for the particular plants you bought; it is a wider layout intended for well-spaced bulb onions.
Water the bed after planting to settle soil around seeds, sets, or roots. Keep the soil consistently moist while the onions establish, but do not leave the bed waterlogged.

Special Raised-Bed Layouts for Mixed Harvests

A raised bed can hold both scallions and bulb onions if you plan the harvest order before planting.

Mark the positions for the onions you want to mature into bulbs first. Then fill selected spaces between them with extra seedlings intended for early green-onion harvest. Pull those young onions before the remaining plants begin to crowd each other.

This approach is especially useful with seed-grown onions. You get an early harvest from thinnings while leaving the strongest, best-spaced plants to form bulbs.

Avoid treating the bed edge as extra planting space. A bulb that develops right against a wooden or metal bed frame can be misshapen and harder to harvest. Keep the outside plants centered within their intended growing space rather than pressing them against the border.

What Happens When Onions Are Planted Too Close

Crowded onions commonly produce smaller bulbs because the plants compete for water, nutrients, and light. Their leaves overlap sooner, weeds are harder to remove, and it becomes difficult to see which plants need thinning.

If seedlings are too close, correct the problem early:

Identify the strongest, healthiest plants to keep.
Pull the extra seedlings gently when the soil is moist enough to release roots easily.
Use pulled seedlings as green onions if they have usable tops and a small white stem.
Remove weeds by hand around the remaining onions so weeds do not take the space and nutrients you created by thinning.
Re-level loose soil around exposed roots.

Sets planted too closely need thinning. Their initial spacing is not necessarily their final bulb spacing, so remove selected plants as they grow to give the remaining onions room to enlarge.

Check Your Onion Bed Before the Bulbs Enlarge

Use this quick check after thinning and again as bulbs begin to swell:

Each remaining onion has open soil around its base rather than being pressed against a neighbor.
Weeds are removed while they are small.
Water reaches the root zone without leaving the bed soggy.
You know which onions are intended for early green-onion harvest and which are staying for bulbs.

Mark the bed with the variety name and planting date. That makes it easier to compare spacing and bulb size at harvest, then improve the layout next season.

Frequently Asked Questions

How Far Apart Should I Plant My Rows of Onions?

Plant standard onion rows 12 to 24 inches apart, with 1 to 8 inches between plants within each row. Use narrower row and plant spacing for scallions or smaller onions, and wider spacing when growing large bulbs. In a raised bed, choose row widths that still let you weed and harvest without stepping on the soil.

How Far From the Edge of a Raised Bed Should I Sow Red Onion Seeds?

Place the first planting line to leave mature plants their intended space from the bed edge. Red onions need the same spacing approach as yellow or white onions; bulb size, not color, determines the final spacing. Sow seeds as needed, then thin the seedlings to the planned positions.

How Deep Should Onion Bulbs Be Planted?

Plant onion sets with the pointed end up and cover them with about 1 inch of soil; some variety directions use a 1- to 2-inch planting depth. Plant rooted onion transplants about 1 inch deep, with roots covered and the leaf neck kept above the soil. Burying transplants too deeply can trap soil and water around the young leaves.

What should you add to the soil before planting onions?

Work mature compost into the upper soil layer if the bed needs more organic matter. Avoid fresh manure and heavy fertilizer applications because excess nitrogen can encourage leaves instead of bulb development.

How close together should onion sets be planted?

Place onion sets 2 to 3 inches apart at first, then thin them as they grow. Leave 4 inches between plants for moderate bulbs or 8 inches for large bulbs.

What can you plant beside onions?

You can grow lettuce alongside onions. This combination is suggested because onions can deter aphids.