How many onions per square metre: planting distance

Why planting distance matters for onions

Onions are slow growers compared to other vegetables. They spend long in the ground before harvest is ready. Smaller distance means more onions per square metre, but onions planted too densely do not grow to full size. You get many small onions instead of a few large healthy ones. Correct planting distance balances yield against quality.

Onions need space to let their bulb expand. The larger the planting distance, the larger each onion. The smaller the distance, the more onions you get, but smaller ones. It is about your preference and how much space you have.

Type 1: Large onions (Allium cepa var. cepa)

Large onions are your typical summer or storage onions. Varieties like 'Stuttgarter', 'Red Baron' and 'Ailsa Craig' grow to full size.

Plant large onions 15-20 cm apart. This gives roughly 3-4 onions per square metre (at 30 cm row spacing). The onion gets room to expand to large format.

Type 2: White and sweet onions

White and sweet onions like 'Candy' and 'Walla Walla' are more precise in growth. They love rich soil and sufficient space.

Plant white onions 15-25 cm apart. Give them more room than red onions if you want large specimens. 2-3 onions per square metre.

Type 3: Shallots (Allium cepa var. aggregatum)

Shallots grow in clusters. Each shallot plant produces a number of small bulblets. Varieties like 'Golden Gourmet' and 'Pikant' are popular.

Plant shallots 20-30 cm apart. They grow larger than regular onions and want more space. Really, even 30-40 cm is not too much. You get 2-3 shallots per square metre.

Type 4: Pearl or pickling onions

Pearl onions are small, compact onions intended for whole pickling. Varieties like 'Paris Silverskin' and 'Barletta' grow small.

Plant pearl onions 8-12 cm apart. They are small, so tight spacing is fine. You get 6-10 small onions per square metre.

TL;DR

• Large onions: 15-20 cm spacing (3-4 per m2)
• White/sweet onions: 15-25 cm spacing (2-3 per m2)
• Shallots: 20-30 cm spacing (2-3 per m2)
• Pearl onions: 8-12 cm spacing (6-10 per m2)

Step-by-step

Step 1: Identify your onion type

Check your seedling or seed packet. Are you planting large onions (green seedlings) or from seed? What is your variety? This determines your spacing.

Step 2: Prepare your bed

Onions love loose, workable soil. Work compost or aged manure in. Ensure good drainage. Onions rot if too wet.

Step 3: Plant at correct distance

• Large onions: 15-20 cm apart
• White/sweet: 15-25 cm apart
• Shallots: 20-30 cm apart
• Pearl onions: 8-12 cm apart

Ensure the top of the onion set is just visible above soil (not buried).

Step 4: Water regularly, no standing water

Onions love moist soil, not wet. Water regularly in dry spells. Ensure good drainage, as onions get disease in waterlogged soil.

Step 5: Thin if needed

If you grow from seed, you can thin. Small seedlings can be removed to give room. Eat them as microgreens or compost them.

Frequently asked questions

How large do onions get at good spacing?

A large onion at 15-20 cm spacing grows to 6-10 cm diameter in ideal conditions. Larger is hard to achieve. Some cultivars naturally grow bigger.

Can I plant onions denser and increase yield?

Not really smart. Onions planted too close do not expand. You get many small onions instead of good size. Plus: dense plantings get less air and disease enters easily.

When do I sow onions, when do I plant?

Sow seed indoors in February/March. Plant seedlings outdoors in April/May. Or buy pre-grown "sets" (small onions) and plant directly. Sets are easier for beginners.

How long do onions take to grow?

From planting to harvest: 90-120 days depending on type and weather. Summer types faster. Winter types slower.

Frequently asked questions

What is the difference between growing onions from sets versus seed?

Sets (small pre-grown onions) are faster, 60-90 days to harvest. Seed is cheaper, 120+ days to harvest. Both work well, it depends on your patience and budget.

Do onions need extra feeding?

Onions are moderate feeders. Compost in the planting hole is usually enough. Light fertiliser water every 3-4 weeks helps for larger specimens. Provide nitrogen early, less later (promotes bulbing).

Can I grow onions in containers?

Yes, large pots (20+ litres) fit 2-3 onions. Use loose potting mix with good drainage. Ensure plenty of sun. Containers dry quickly, so water regularly.

Discover your vegetable bed

At [gardenworld.app](https://gardenworld.app) you can visualise your vegetable garden with correct planting distances for onions and other vegetables. See what your harvest looks like before you plant.