Onion Sets: What They Are, How to Plant Them, and Tips for Success

Onion sets are small, immature onion bulbs grown from seeds during the previous season and are one of the easiest ways to grow onions. They are ideal for gardeners looking for a quick and reliable method to produce large, flavorful onions without starting from seeds. Onion sets are widely available and can be planted directly into your garden, making them perfect for beginner and experienced gardeners alike.

This guide explains what onion sets are, how to plant and care for them, and tips for a successful onion harvest.

What Are Onion Sets?

Definition

Onion sets are small, partially grown onion bulbs that can be planted directly into the soil to grow into mature onions. They are usually the second stage of onion growth after seeds but before full maturity.

Key Features

• Ease of Use: Require minimal preparation and are easy to plant.
• Faster Growth: Grow more quickly than onions started from seeds.
• Common Varieties: 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 directly in the soil without the need for germination or indoor sowing.

2. Faster Harvest

• Sets grow faster than onions started from seeds, often maturing in 90–120 days.

3. Reliable Growth

• Onion sets are less prone to pests, diseases, and poor weather conditions compared to seedlings.

4. Ideal for Beginners

• Perfect for gardeners with limited experience or those looking for a low-maintenance crop.

Types of Onion Sets

1. Yellow Onion Sets:
   • Mild, versatile onions suitable for cooking and storage.
2. Red Onion Sets:
   • Sweet and colorful, ideal for salads and raw dishes.
3. White Onion Sets:
   • Crisp and mild onions commonly used in cooking and pickling.

When to Plant Onion Sets

Spring Planting:

• Plant onion sets in early spring (March–April) once the soil is workable and the risk of frost has passed.

Autumn Planting:

• For overwintering varieties, plant sets in late summer to early autumn (August–September). These will mature in early 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.
• Choose a sunny spot, 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 end facing up.
3. Cover the sets lightly with soil, ensuring the tops are just visible above the soil surface.

3. Watering

• Water immediately after planting to help the sets settle into the soil.
• Keep the soil consistently moist but not waterlogged during the growing season.

Caring for Onion Sets

1. Watering

• Provide consistent moisture, especially during dry spells, to encourage bulb development.
• Reduce watering once the tops begin to yellow and fall over to prevent rot.

2. Fertilizing

• Apply a balanced fertilizer high in nitrogen every 2–3 weeks during early growth.
• Switch to a low-nitrogen fertilizer as the bulbs start to form.

3. Weeding

• Keep onion beds free from weeds, which compete for nutrients and water.

4. Mulching

• Use mulch to retain soil moisture and suppress weed growth.

5. Pest and Disease Management

• Protect onion sets from onion flies, thrips, and aphids using netting or organic insecticides.
• Avoid overwatering to reduce the risk of fungal diseases like downy mildew and white rot.

Harvesting Onions from Sets

Spring Onions

• Harvest immature onions early as green onions or scallions, typically 4–6 weeks after planting.

Bulb Onions

• Onions are ready to harvest when the tops turn yellow and begin to fall over.
• Gently lift the bulbs using a fork and allow them to dry in a sunny, well-ventilated area for 1–2 weeks.

Storing Onions Grown from Sets

1. Curing:
   • Allow harvested onions to dry and cure completely before storing to prevent rot.
2. Storage:
   • Store cured onions in a cool, dry, and dark place with good ventilation, such as a mesh bag or basket.

Tips for Planting and Growing Onion Sets

1. Choose Quality Sets: Select firm, disease-free sets from a reputable supplier.
2. Avoid Planting Too Deep: Plant sets shallowly, with the tips just visible above the soil.
3. Rotate Crops: Avoid planting onions in the same spot each year to reduce disease risks.
4. Protect from Frost: Use cloches or fleece to shield young plants from unexpected frost.

Common Problems with Onion Sets

1. Bolting

• Onion sets may bolt (produce flowers) if planted too early or exposed to stress.
• Solution: Plant at the right time and keep the soil consistently moist.

2. Poor Bulb Formation

• Causes: Overcrowding, poor soil fertility, or insufficient sunlight.
• Solution: Thin plants and ensure proper spacing and fertilization.

3. Pests and Diseases

• Onion Fly: Larvae can damage bulbs. Use netting for protection.
• White Rot: A fungal disease that affects bulbs and roots. Avoid planting onions in infected soil.

Top 10 Questions About Onion Sets

1. What are onion sets?

Onion sets are small, immature onion bulbs grown from seeds and used for quick and easy planting.

2. When should I plant onion sets?

Plant sets in early spring for summer harvests or in late summer for overwintering varieties.

3. How deep should I plant onion sets?

Plant onion sets shallowly, with the tips just visible above the soil.

4. How far apart should onion sets be planted?

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. Do onion sets need a lot of water?

Onions need consistent moisture but should not be overwatered to prevent rot.

7. Can I grow onion sets in containers?

Yes, onion sets can be grown in containers with at least 20 cm depth and good drainage.

8. Why are my onion sets bolting?

Bolting occurs due to stress or planting too early. Plant at the correct time and ensure consistent care.

9. How do I store harvested onions from sets?

Cure the onions by drying them for 1–2 weeks, then store in a cool, dry, and dark place.

10. Can onion sets be planted in autumn?

Yes, overwintering varieties of onion sets can be planted in late summer to early autumn for an early spring harvest.

Conclusion

Onion sets offer a quick, easy, and reliable way to grow onions, making them an excellent choice for gardeners of all skill levels. With minimal preparation and care, you can enjoy a bountiful harvest of flavorful onions for cooking and storage. By selecting the right varieties, planting at the right time, and following proper care techniques, you’ll set yourself up for success with onion sets in your garden.