How to Harvest Onion Sets

Harvesting onion sets is a straightforward process that ensures a fresh and abundant supply of onions for future planting or cooking. Onion sets are small, immature onion bulbs that are grown specifically for replanting. Proper harvesting techniques play a crucial role in preserving their quality and maximizing their potential for growth in the next planting season. This guide aims to provide a clear and straightforward explanation of how to harvest onion sets. 

What Are Onion Sets

Onion sets are small, partially grown onion bulbs that are cultivated primarily for planting in the next growing season. These sets are typically started from seeds or seedlings and allowed to grow until they reach a specific, immature size before being harvested. Their small size and dormant state make them ideal for easy planting and storage. Onion sets offer a fast and reliable way to grow onions compared to starting from seeds, as they have already undergone part of the growing process and are less prone to environmental stress or pests. This makes them a popular choice among gardeners looking for a head start when cultivating onions.

Difference Between Onion Sets and Full-Sized Onions

Onion sets and full-sized onions serve different purposes and are at distinct stages of growth. Onion sets are small, immature onion bulbs that have been purposely cultivated to be replanted in a subsequent season. They are harvested before reaching full maturity and are ideal for gardeners who want a quick and reliable way to grow onions without starting from seeds. On the other hand, full-sized onions are mature bulbs harvested when they have reached their maximum growth.

These are ready to be consumed immediately and are used widely in cooking due to their fully developed flavor and size. While onion sets are primarily used for propagation, full-sized onions are valued as a final, edible product. Understanding this distinction helps in selecting the best option based on gardening or culinary needs.

10 Methods How to Harvest Onion Sets

1. Monitor the Onion Tops for Signs of Maturity

The first and most crucial step in harvesting onion sets is to closely observe the tops of the onion plants. Onion sets are typically ready for harvest when their green tops start to yellow, bend over, and eventually fall down naturally. This indicates that the plant has completed its growth cycle and that the nutrients have moved from the leaves into the small bulbs below the soil. It’s important to wait until at least 50 to 75 percent of the tops have fallen over before you begin harvesting. Rushing this process can result in immature, underdeveloped sets that won’t store well or produce strong crops when replanted.

Always harvest when the weather is dry to prevent rot and mold from developing on the bulbs.

2. Choose the Right Time of Day

Timing your harvest during the correct part of the day helps protect your onion sets from moisture and damage. It is best to harvest in the morning after the dew has evaporated, or in the early evening when the sun is not at its peak. Harvesting during these times ensures that the soil is relatively dry, which helps minimize the risk of fungal infection and allows for easier digging. Avoid harvesting immediately after a heavy rain, as wet soil can cling to the bulbs, increasing the chances of rot and disease. Proper timing not only makes the process easier but also safeguards the quality of the onion sets for storage or future planting.

3. Loosen the Soil Gently Before Pulling

To avoid damaging the delicate sets, use a garden fork or hand trowel to carefully loosen the soil around each plant. Insert the tool a few inches away from the base of the plant to prevent slicing into the bulbs. Gently lift the plant and shake off any excess dirt without brushing or scrubbing the bulbs too harshly. Onion sets are more fragile than mature onions, and bruising them during harvest can cause them to rot in storage. Loosening the soil ensures that you can remove them without resistance, keeping the skin intact and the necks firm and dry.

4. Sort Out Bolted or Damaged Sets

After pulling the onion sets from the soil, take a few minutes to inspect them closely. Sets that have bolted—meaning they’ve grown a flower stalk—should be separated because they’re less suitable for replanting. Bolting can indicate stress or premature maturity, which reduces their productivity in the next growing cycle. Similarly, remove any bulbs that are bruised, moldy, soft, or split. These damaged sets can infect healthy ones during storage and reduce your overall yield. Sorting the sets during harvest helps you maintain a collection of only the healthiest, most viable bulbs for planting or storage.

5. Allow the Onion Sets to Cure Properly

Curing is a vital post-harvest step that helps dry out the onion sets and toughen their outer skins, improving shelf life. Lay the freshly harvested sets in a single layer on a wire rack, mesh screen, or flat surface in a dry, shaded, and well-ventilated area. Avoid direct sunlight, which can scald the bulbs or cause them to dry too quickly and split. Let them cure for at least 7 to 10 days, turning them occasionally to ensure even drying. You’ll know they’re ready when the outer skin is dry and papery and the neck feels firm and closed. Proper curing minimizes the risk of fungal issues and helps the sets store safely for several months.

6. Clean the Onion Sets Carefully

Once the onion sets have been properly cured, you can gently clean them to remove excess soil and any loose outer layers. Do not wash the sets with water, as moisture can lead to spoilage. Instead, use your hands to brush off any remaining dirt. If the outer layers are particularly dirty or peeling, you can remove them by hand, but avoid taking off too much of the protective skin. Keeping some of the natural covering helps protect the bulb during storage. Remember, the cleaner and drier the sets are, the better their chances of lasting until the next planting season.

7. Size the Onion Sets for Future Use

After cleaning, it’s helpful to sort the onion sets by size. Small sets, typically no larger than ¾ inch in diameter, are best suited for planting. They tend to bolt less and develop into strong, uniform onions. Medium to large sets may be used in the kitchen or preserved for short-term use, but they are more likely to bolt when replanted. By sorting them by size, you ensure consistency in your next crop and reduce the chance of uneven growth. Labeling and organizing by size also makes it easier to plan your garden layout when replanting time comes around.

8. Store in a Cool, Dry, and Dark Place

Storing your onion sets correctly is critical to maintaining their viability. After curing and sorting, place them in breathable containers such as mesh bags, paper bags, or shallow cardboard boxes with ventilation holes. Store these in a cool, dry, and dark location, ideally between 32°F to 40°F (0°C to 4°C). Excess warmth or humidity can trigger sprouting or rot. Avoid plastic containers, which trap moisture and encourage mold. Periodically inspect your stored sets to remove any that show signs of softening or decay. Proper storage ensures that your sets stay firm and dormant until planting season arrives.

9. Record the Harvest Details for Future Planning

Keeping a written or digital record of your onion set harvest can significantly improve your gardening efforts in future seasons. Note the variety harvested, the date of harvest, any issues encountered (such as pests or bolting), and how well the sets cured and stored. This data helps you track patterns in growth and harvest success, choose the most productive varieties, and refine your gardening techniques year after year. Detailed records also allow you to plan crop rotations and avoid soil-borne diseases that can affect onions and other alliums.

10. Replenish Soil Nutrients After Harvest

After you finish harvesting your onion sets, don’t forget to care for the soil where they were grown. Onions are heavy feeders, meaning they deplete nutrients in the soil as they grow. Add compost, well-rotted manure, or an all-purpose organic fertilizer to replenish the nutrients before planting another crop. Tilling the soil and allowing it to rest or plant a cover crop like clover can also help rejuvenate it. Maintaining healthy, fertile soil is essential for the success of future onion crops or any other vegetables you may wish to plant in the same bed.

Conclusion

Proper soil management is the foundation of a thriving vegetable garden. By understanding the nutritional needs of crops like onions and taking steps to replenish and maintain soil fertility, you can ensure a bountiful harvest season after season. Remember to rotate crops, use organic amendments, and allow the soil to rest when needed. Follow these simple instructions outlined in this blog post about how to harvest onion sets, and you’ll be able to get the job done with ease.