Last Updated on: February 12, 2026

How Far Apart to Plant Onion Sets

Knowing how far apart to plant onion sets is essential for growing healthy onions with good-sized bulbs. Plant them too close and they compete for nutrients; too far apart and you waste valuable growing space.

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Onions are a staple crop for gardens and allotments — easy to grow and brilliant for long-term storage when done right.

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This guide explains the correct spacing for onion sets in the UK, including row spacing, container growing, and how spacing affects bulb size and yield.

Why Spacing Onion Sets Correctly Matters

Correct spacing helps onions to:

Develop full-sized bulbs
Access enough light, water, and nutrients
Reduce disease risk
Grow evenly and mature at the same time

Poor spacing is a common reason onions fail to bulk up properly.

For a complete overview of onion growing from start to finish, see ONION SETS UK: THE COMPLETE GUIDE TO PLANTING, GROWING & HARVESTING ONIONS.

Recommended Spacing for Onion Sets in the UK

For most UK gardens, the ideal spacing is:

Between onion sets: 10–15 cm
Between rows: 25–30 cm

This spacing allows each plant enough room to form a good bulb while still using space efficiently.

Does Spacing Affect Onion Size?

Yes — spacing has a direct impact on bulb size.

Closer spacing: Smaller onions, higher total yield
Wider spacing: Larger onions, fewer bulbs

If you want large onions for storage, use the wider end of the spacing range. For smaller onions or pickling, closer spacing works well.

If you’re choosing varieties for size or storage, see BEST ONION VARIETIES FOR UK GARDENS.

How Deep Should Onion Sets Be Planted?

Depth matters just as much as spacing.

Push onion sets into the soil so the tip is just showing
Do not bury the entire bulb
Firm soil gently around the base

Planting too deeply can slow growth, while planting too shallow may cause sets to dry out or be disturbed by birds.

For planting timing advice, see WHEN TO PLANT ONION SETS IN THE UK.

Spacing Onion Sets in Raised Beds

Raised beds are ideal for onions because they offer good drainage and warm up quickly.

In raised beds:

Keep to 10–15 cm spacing
Stagger planting slightly for efficient use of space
Avoid overcrowding edges

If you grow in raised beds regularly, you may also find HOW TO GROW ONIONS IN CONTAINERS useful for flexible layouts.

Spacing Onion Sets in Containers

Onions grow well in containers if spaced correctly.

In containers:

Allow one onion per 10–15 cm
Use wide, shallow containers rather than deep pots
Ensure good drainage

Overcrowding in containers leads to small bulbs and weak growth.

What Happens If Onion Sets Are Planted Too Close Together?

Planting onion sets too close can cause:

Small or misshapen bulbs
Increased competition for nutrients
Poor airflow
Higher disease risk

Overcrowding can also stress plants, which increases the risk of bolting. Learn how to prevent this in WHY ONIONS BOLT AND HOW TO STOP IT.

Should You Thin Onion Sets?

Onion sets rarely need thinning if spaced correctly at planting time.

If you do see overcrowding:

Remove the weakest plants early
Use removed onions as spring onions
Avoid disturbing neighbouring roots

Does Spacing Change With Planting Time?

Spacing stays the same whether planting in February, March, or April.

However, correct spacing becomes even more important if planting early, as stressed plants are more likely to bolt.

If you’re planting early, see CAN YOU PLANT ONION SETS IN FEBRUARY.
For the most reliable results, read CAN YOU PLANT ONION SETS IN MARCH.

Summary: How Far Apart Should You Plant Onion Sets?

Ideal spacing: 10–15 cm apart
Row spacing: 25–30 cm
Wider spacing: Larger bulbs
Closer spacing: Smaller bulbs, higher yield

For everything else you need to know about growing onions successfully, return to ONION SETS UK: THE COMPLETE GUIDE TO PLANTING, GROWING & HARVESTING ONIONS.

Related Onion Growing Guides

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