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

Onion sets are one of the easiest ways to grow onions in your garden, offering a quick and reliable method for both beginner and experienced gardeners. Onion sets are small, immature onion bulbs that can be planted directly into the soil, making them a popular choice for UK gardeners looking for convenience and consistent results.

This guide explains everything you need to know about onion sets in the UK, including planting tips, care, harvesting, and the best varieties to grow.

What Are Onion Sets?

Definition

Onion sets are partially grown onion bulbs from the previous season, harvested early and stored to be replanted. These sets allow for faster onion growth compared to starting from seeds.

Key Features

• Ease of Planting: Simple to plant directly into the soil.
• Faster Harvest: Mature more quickly than onions grown from seeds.
• Variety Options: Available in red, yellow, and white onion types.

Advantages of Using Onion Sets

1. Quick and Easy to Plant
   • Onion sets are ready to plant straight into the soil, requiring minimal preparation.
2. Reliable Growth
   • Less prone to pests and diseases compared to seedlings.
3. Faster Harvest
   • Grow to maturity in about 90–120 days, faster than onions from seeds.
4. Ideal for Beginners
   • A great option for gardeners with limited experience or time.

Popular Onion Set Varieties in the UK

1. Red Baron: A mild, sweet red onion with deep crimson skin, perfect for salads.
2. Sturon: A classic yellow onion known for its excellent storage life.
3. Centurion: An early-maturing variety with golden skin and robust flavor.
4. Snowball: A white onion with a mild taste, ideal for cooking and pickling.
5. Radar: A hardy overwintering variety that produces large, sweet onions.

When to Plant Onion Sets in the UK

Spring Planting

• Timing: March to April
• Why: Planting in spring allows sets to establish roots and grow quickly as temperatures warm.

Autumn Planting

• Timing: Late August to September
• Why: Overwintering onion sets, such as Radar and Senshyu, can be planted in autumn to mature the following spring.

How to Plant Onion Sets

1. Prepare the Soil

• Onions thrive in well-drained, fertile soil with a pH of 6.0–6.8.
• Add compost or well-rotted manure to enrich the soil before planting.
• Choose a sunny location, as onions require full sun for optimal growth.

2. Planting the Sets

1. Make shallow holes or furrows in the soil, spacing them 10–15 cm apart in rows 30 cm apart.
2. Place the onion sets in the holes with the pointed side facing up.
3. Cover with soil, leaving the tops of the sets just visible.

3. Watering

• Water thoroughly after planting to help the sets settle.
• Keep the soil consistently moist, but avoid waterlogging.

Caring for Onion Sets

1. Watering

• Provide consistent moisture during the growing season, especially in dry spells.
• Reduce watering as the bulbs begin to mature to prevent rot.

2. Fertilizing

• Apply a balanced fertilizer every 2–3 weeks during early growth.
• Stop fertilizing once the bulbs start forming.

3. Weeding

• Keep onion beds weed-free to reduce competition for nutrients and water.

4. Mulching

• Apply mulch to retain soil moisture, regulate temperature, and suppress weeds.

5. Pest and Disease Management

• Pests: Protect onion sets from onion flies, thrips, and aphids using netting or organic sprays.
• Diseases: Prevent fungal infections like downy mildew and white rot by ensuring good air circulation and avoiding waterlogged soil.

Harvesting Onions Grown from Sets

1. Spring Onions:
   • Harvest young plants as green onions 4–6 weeks after planting.
2. Bulb Onions:
   • Mature onions are ready to harvest when the tops turn yellow and begin to fall over, typically in mid-to-late summer.
   • Gently lift the bulbs with a garden fork and leave them to dry in a sunny, well-ventilated spot for 1–2 weeks.

Storing Onions

1. Curing:

• Allow harvested onions to cure in a warm, dry place for 1–2 weeks to enhance their storage life.

2. Storage:

• Store cured onions in a cool, dry, and dark location with good ventilation, such as mesh bags or baskets.

Tips for Planting and Growing Onion Sets in the UK

1. Choose the Right Variety: Select varieties suited to your planting season, such as overwintering types for autumn or standard sets for spring.
2. Plant Shallowly: Ensure the tops of the sets are just visible above the soil surface.
3. Rotate Crops: Avoid planting onions in the same spot as the previous year to reduce disease risks.
4. Protect from Frost: Use cloches or fleece to shield young plants in colder regions.
5. Monitor Moisture: Keep the soil moist during the growing season but avoid overwatering.

Common Problems with Onion Sets

1. Bolting

• Cause: Planting too early or stress from fluctuating temperatures.
• Solution: Plant sets at the correct time and keep soil consistently moist.

2. Poor Bulb Formation

• Cause: Overcrowding or insufficient sunlight.
• Solution: Thin plants and ensure proper spacing and full sun.

3. Pests and Diseases

• Common Issues: Onion flies, thrips, and fungal diseases like white rot.
• Solution: Use netting for protection and rotate crops to avoid disease buildup.

Top 10 Questions About Onion Sets in the UK

1. What are onion sets?

Onion sets are small, immature onion bulbs that are replanted to grow into full-sized onions.

2. When should I plant onion sets in the UK?

Plant onion sets in early spring (March to April) or overwintering varieties in late summer to early autumn (August to September).

3. How deep should I plant onion sets?

Plant sets shallowly, with the tops just visible above the soil.

4. How far apart should onion sets be spaced?

Space sets 10–15 cm apart in rows 30 cm apart.

5. How long do onions from sets take to grow?

Onions from sets typically take 90–120 days to mature.

6. Can I grow onion sets in containers?

Yes, onion sets can be grown in containers with sufficient depth and good drainage.

7. What are the best onion sets for the UK?

Popular varieties include Red Baron, Sturon, Radar, and Senshyu.

8. Do onion sets need a lot of water?

Onions need consistent moisture, but overwatering should be avoided to prevent rot.

9. How do I prevent bolting in onion sets?

Plant at the right time, keep the soil moist, and avoid temperature stress.

10. How do I store onions after harvesting?

Cure onions for 1–2 weeks, then store them in a cool, dry, and ventilated place.

Conclusion

Onion sets are a simple and effective way to grow onions in the UK, offering quick results and reliability. By choosing the right varieties, planting at the correct time, and providing proper care, you can enjoy a successful onion crop with minimal effort. Whether you’re a beginner or a seasoned gardener, onion sets are an excellent choice for growing fresh, flavorful onions.