Growing onions looks easy on the surface. You plant them, water them, wait — and expect big, firm bulbs at harvest. Yet many gardeners end up with onions that stay small, split early, or put all their energy into leaves instead of bulbs.

The truth is, onions are sensitive plants. Small details at planting time can make a big difference later. One simple adjustment — often overlooked — can help onions focus their energy where it matters most: underground, into the bulb.

Why onions sometimes stay small

Onions grow in two phases:

1. Leaf growth – Above ground
2. Bulb formation – Below ground

If the plant is stressed, planted incorrectly, or crowded, it may:

• Keep producing leaves instead of forming a bulb
• Split into multiple small bulbs
• Stop growing early

Most of these problems start at planting time, not later in the season.

The simple trick: plant onions shallow and spaced wider than you think

The most effective (and simplest) trick for bigger onions is this:

👉 Plant onions shallow, with the top of the bulb just barely covered, and give them generous spacing.

This goes against what many people instinctively do — planting too deep and too close together.

Why this works

• Shallow planting keeps the bulb warm and dry
• Good airflow around the bulb reduces rot and disease
• More space allows each onion to fully expand
• Sun exposure at the bulb neck signals the plant to bulk up

Onions don’t want to be buried. They want room.

How to plant onions the right way (step by step)

1. Choose the right type for your area

Use short-day, long-day, or intermediate onions depending on your latitude. This affects bulb size more than fertilizer ever will.

2. Prepare loose soil

Onions prefer:

• Loose, well-draining soil
• No compacted clumps
• Light compost mixed in (not fresh manure)

Hard soil physically restricts bulb growth.

3. Plant shallow

Whether using:

• Onion sets
• Seedlings
• Transplants

Plant them so that:

• Roots are covered
• The bulb tip is at or just above soil level

You should still be able to see the top.

4. Space generously

This is where most people go wrong.

For big bulbs:

• 4–6 inches apart minimum
• Rows at least 12–15 inches apart

Crowded onions compete. Spacious onions grow.

One extra step that helps even more: trim before planting

If you’re planting onion transplants or sets with long tops:

✂️ Trim the green tops to about 3–4 inches before planting

This:

• Reduces transplant shock
• Encourages root establishment
• Helps the plant redirect energy downward

This doesn’t hurt the onion — it helps it settle faster.

Watering: steady, not heavy

Onions like consistency.

• Water deeply but not constantly
• Avoid waterlogged soil
• Reduce watering once bulbs start swelling

Too much water late in the season can cause:

• Soft bulbs
• Poor storage quality

Let the soil dry slightly between watering.

What NOT to do if you want big onions

🚫 Don’t plant too deep
🚫 Don’t crowd plants
🚫 Don’t over-fertilize with nitrogen
🚫 Don’t mulch heavily over the bulb

Nitrogen-heavy fertilizer late in the season produces leaves, not bulbs.

Mulch — but only around, not over

Mulch helps retain moisture and suppress weeds, but keep it:

• Around the onion, not covering the bulb
• Light and loose

Bulbs should still see daylight.

When onions really start bulking up

Onions begin forming bulbs when day length triggers them. At this stage:

• Growth happens fast
• Spacing becomes critical
• Stress reduces final size

If planted shallow and spaced correctly, onions can double in size during this phase.

Signs you’re doing it right

You’ll notice:

• Bulbs pushing slightly above soil
• Thickening at the base
• Strong upright leaves
• Uniform bulb size across the row

This is exactly what you want.

Harvesting matters too

For the biggest, best onions:

• Let tops fall over naturally
• Don’t force them down early
• Harvest on a dry day
• Cure in a warm, airy place

Good planting leads to good harvesting.

Why this trick works year after year

This method doesn’t rely on:

• Expensive fertilizer
• Special products
• Complicated techniques

It works because it respects how onions naturally grow.

Big onions aren’t forced — they’re allowed.

If you’ve struggled with small onions in the past, don’t blame your soil, your weather, or your luck just yet. Often, the difference between tiny bulbs and a generous harvest comes down to how deep and how close you plant them.

Plant shallow. Give space. Let the bulb breathe.

Sometimes the simplest gardening tricks really do make the biggest difference.