🧅🌱 Sowing Onion Seeds from Saved Seed (UK Guide)

🌱 Introduction: Can You Grow Onions from Saved Seed?

Yes—you can sow onion seeds saved from your own plants, but there are important differences compared with using bought seed. Onion seeds lose viability quickly, and saved seed can behave differently depending on variety, age, and how it was collected.

This guide explains when saved onion seed is worth using, how to test it, how to sow it successfully, and what results to expect in UK conditions.

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• Seed Compost & Propagator

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🌼 First: Where Did the Saved Seed Come From?

Onion seed should only be saved from:

• Fully mature onions that flowered and set seed
• Healthy, vigorous plants
• Open-pollinated varieties (not F1 hybrids)

⚠️ Important warning

• F1 hybrid onions do not come true from seed
• Saved seed from F1s may grow poorly, bolt early, or produce uneven bulbs

If you don’t know the variety, expect variable results.

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⏳ How Long Do Onion Seeds Stay Viable?

Onion seeds have a short shelf life.

Seed age	Expected viability
Fresh (same year)	Very good
1 year old	Fair
2 years old	Poor
3+ years old	Usually unreliable

👉 If your saved seed is over 1 year old, expect lower germination and sow more thickly.

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🧪 Do a Germination Test First (Highly Recommended)

Before sowing properly:

1️⃣ Place 10 seeds on damp kitchen paper
2️⃣ Seal in a plastic bag
3️⃣ Keep warm (15–20°C)
4️⃣ Check after 10–14 days

Results:

• 7–10 sprouted → good seed
• 4–6 sprouted → sow thicker
• Fewer than 4 → consider replacing seed

This saves weeks of wasted space.

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📅 When to Sow Saved Onion Seed (UK)

Because saved seed is often weaker:

• Mid–late February → best and safest
• Early March → still reliable
• January sowing only with grow lights and experience

Avoid very early sowing—weak seed + low light = failure.

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🌱 Compost Choice (Even More Important with Saved Seed)

Use fine seed compost only.

Why:

• Encourages faster, even germination
• Reduces rot risk
• Supports weaker seeds

Avoid:

• Garden soil
• Rich compost
• Old reused compost

Saved seed is less forgiving of poor conditions.

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🌱 How to Sow Onion Seeds from Saved Seed

1️⃣ Sow Slightly Thicker Than Normal

Because germination may be uneven:

• Sow closer together than shop-bought seed
• You can thin later

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2️⃣ Sow Shallow

• Cover with 5–10 mm of compost or vermiculite
• Never bury deeply

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3️⃣ Water Gently

• Compost damp, not wet
• Cold, soggy compost kills weak seed fast

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4️⃣ Place Somewhere Bright & Cool

• 15–20°C for germination
• Cool and bright after emergence

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⏳ Germination Time from Saved Seed

Expect:

• 10–21 days
• Often slower and less even than fresh seed

👉 Do not resow for at least 3 weeks.

Patchy emergence is normal with saved seed.

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🌿 Seedling Care (Be Gentle)

Once seedlings appear:

• Give maximum light
• Keep temperatures 10–15°C
• Water sparingly
• Ensure airflow

Saved-seed seedlings may grow unevenly—this is normal early on.

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✂️ Trimming Seedlings (Helps Weak Plants)

When seedlings reach 12–15 cm:

• Trim back to 8–10 cm

This:

• Strengthens stems
• Reduces stress
• Helps weaker plants catch up

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🌱 Thinning & Selecting the Best Plants

Saved seed often produces variation.

When thinning:

• Keep the strongest, upright seedlings
• Remove weak, twisted, or slow plants
• Don’t feel bad discarding extras

Selection improves your final crop quality.

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🌼 What to Expect at Harvest

From saved seed, you may see:

• More variation in bulb size
• Slightly higher bolting risk
• Differences in storage quality

That doesn’t mean failure—just natural genetic variation.

Many gardeners deliberately save seed to select and improve strains over time.

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🚫 Common Mistakes with Saved Onion Seed

• Using very old seed without testing
• Sowing too early
• Overwatering cold compost
• Expecting uniform results
• Saving seed from hybrid onions

Most problems come from seed age + impatience.

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🧠 Key Takeaway

Sowing onion seeds from saved seed can work very well, especially if the seed is fresh and from open-pollinated varieties. Expect slower, more uneven germination, sow slightly thicker, and thin carefully.

If you treat saved seed gently and grow seedlings cool and bright, you can still raise strong onions and even improve your own strain over time.

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