Last Updated on: November 27, 2025

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🧅 Onion Sets UK: A Guide to Planting and Growing Onions from Sets

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🌱 Introduction: Why Grow Onions from Sets?

Onion sets are the easiest and most reliable way to grow onions in the UK. They’re small, immature onions that you plant directly into the soil, making onion-growing simple even for total beginners.

Growing onions from sets gives you:

• quicker results than seeds
• stronger, more reliable bulbs
• excellent success in UK weather
• low-maintenance care
• great yields in small spaces

Below are the best sets and tools to help you grow perfect onions at home or on the allotment.

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⭐ Check Out Our Recommended Products

• Onion Sets (Red, White & Yellow Varieties)

Reliable, beginner-friendly and perfect for UK climates.
Click here to see them

• Multi-Purpose Compost + Grit

Improves drainage and prevents rotting.
Click here to see them

• Netting or Fleece for Protection

Stops birds from pulling out newly planted sets.
Click here to see them

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🧅 When to Plant Onion Sets in the UK

You can plant onion sets in two main seasons:

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🍁 1️⃣ Autumn Planting (Overwintering Sets)

Planting time: September – November

Great for producing early summer onions.
Choose hardy varieties such as:

✔ Radar
✔ Senshyu Yellow
✔ Electric Red

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🌸 2️⃣ Spring Planting (Most Common)

Planting time: February – April

Perfect for beginners and very reliable.
Choose varieties such as:

✔ Sturon
✔ Stuttgarter
✔ Red Baron
✔ Centurion

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🌿 How to Plant Onion Sets Step-by-Step

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1️⃣ Prepare the Soil

Onions prefer:

✔ full sun
✔ fertile but free-draining soil
✔ minimal competition from weeds

Improve heavy or clay soils with:

• compost
• grit
• well-rotted manure (add in autumn, never fresh)

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2️⃣ Plant Each Set Pointy-End Up

This is essential.

Planting depth:

👉 Just below the soil surface
(You should just see the tip poking through.)

Spacing:

• 10 cm between sets
• 30 cm between rows

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3️⃣ Water Lightly

Water once after planting, then sparingly.

Too much moisture causes rot, especially in cold weather.

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4️⃣ Protect from Birds

Birds love pulling up onion sets.

Use:

• fleece
• netting
• cloches

Once roots establish, the sets stay firmly in place.

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5️⃣ Keep the Area Weed-Free

Onions hate competition.

Weed regularly to help bulbs grow large and even.

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🌞 Caring for Onion Sets Through the Season

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✔ Water During Dry Spells

Onions need consistent moisture but not waterlogging.

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✔ Feed Once or Twice

Use a high-potash fertiliser during mid-growth.
Avoid nitrogen-rich feeds — they cause soft growth and disease.

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✔ Loosen Soil Around Bulbs

As onions swell, gently ease soil away to help bulbs fatten evenly.

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✔ Stop Watering 2–3 Weeks Before Harvest

This helps skins dry and bulbs cure properly.

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🌾 When to Harvest Onions from Sets

Harvest time depends on planting season:

🔹 Autumn-planted sets:

👉 June – July

🔹 Spring-planted sets:

👉 July – August

Signs onions are ready:

✔ leaves yellow and fall over
✔ bulbs feel firm
✔ necks dry out

Once the tops have completely fallen, lift the onions and dry them.

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🌬 How to Dry and Store Onions

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✔ Cure for 2–3 Weeks

Lay onions in a warm, airy place.

Do not wash — brush off soil gently.

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✔ Trim and Store

Cut stems to 2–3 cm and store in:

• nets
• trays
• braids

Good onions can store for 4–8 months.

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❌ Common Problems with Onion Sets

❌ Sets rotting

Soil too wet or clay-heavy.

❌ Sets bolting

Cold stress or poor-quality stock.

❌ Small bulbs

Planted too close together or lack of sunlight.

❌ Leaves yellowing early

Possible onion fly or nutrient deficiency.

❌ Mildew

Too much moisture and poor air circulation.

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🌼 FAQs

Can I plant supermarket onions as sets?

No — they won’t grow properly and may carry diseases.

Should onion sets be covered fully?

No — leave the tip visible.

Do onions need full sun?

Yes — sun helps bulbs grow and ripen.

Can I grow onion sets in pots?

Yes — use deep containers with grit for drainage.

How long do onions take to grow from sets?

About 20–26 weeks, depending on variety and season.

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