Essential Tips for Growing Onion Sets: A Comprehensive Guide

Welcome to our comprehensive guide on growing onion sets! Whether you are a seasoned gardener or just starting out, following these essential tips will help ensure a successful crop of delicious onions. In this article, we will cover the basics of onion set gardening and provide expert advice on soil selection, planting techniques, caring for your plants, pest and disease control, harvesting, storage, and troubleshooting common problems. Let’s get started with our top tips for growing onion sets!

Understanding Onion Sets: What Are They and Why Should You Use Them?

Onion sets are small, immature onions that are grown from seed for one year and then harvested. They are ideal for gardeners who want to grow onions but don’t have the time or space to start from seeds. Onion sets come in different sizes, with the smaller ones being more convenient for planting and yielding smaller onions, while the larger ones are known to produce bigger onions.

Onion sets are a popular choice for gardeners because they:

1. Mature earlier than onions grown from seed, meaning you can enjoy fresh onions sooner in the growing season.
2. Are easier and less time-consuming to plant than onion seeds.
3. Have a higher success rate than onion seeds due to their size and ability to establish roots quickly.

If you’re looking for a quick and easy way to grow onions in your garden, using onion sets is an excellent option to consider.

Choosing and Preparing the Right Soil for Onion Sets

One of the most important factors in successfully growing onion sets is selecting and preparing the right soil. Onion sets thrive in loose, well-draining soil that is rich in organic matter.

Before planting, it is important to test the pH of the soil and adjust it if necessary. A pH of 6.0-7.5 is ideal for onion sets. If your soil is too acidic, add lime to raise the pH. If it is too alkaline, add sulfur to lower the pH.

It is also important to ensure that the soil has good drainage. If your soil tends to be compacted and clay-like, you can amend it with sand, peat moss, or perlite to improve drainage.

In addition to improving drainage, adding organic matter to your soil can help provide essential nutrients to your onion sets. Compost, aged manure, and leaf mold are all good options for adding organic matter. Mix in a 2-3 inch layer of organic matter before planting.

Finally, take care not to plant onion sets in soil that has recently been used to grow other alliums, such as garlic or shallots. These plants can leave behind soil-borne diseases that can harm your onion sets.

When and Where to Plant Onion Sets: Seasonal Considerations

Planting onion sets at the right time and in the right location is crucial for a successful harvest. The best time to plant onion sets depends on your local climate, but generally, they should be planted in early spring when the soil has warmed up to a temperature of at least 50°F (10°C). Onions prefer cooler weather, and planting too late in the season can result in smaller bulbs or bolting.

When selecting a location for planting, choose a spot that receives full sun and has good drainage. Avoid planting onions in areas where water tends to collect or in soil that is heavily compacted or has a high clay content.

Temperature Requirements

Onion sets need consistent temperatures between 55°F (13°C) and 75°F (24°C) to germinate and grow properly. If the temperature drops below this range, the growth of the onion sets will slow down, and they may become more susceptible to disease. Conversely, if the temperature is too high, the onion sets may bolt, resulting in reduced yield and smaller bulbs.

Sunlight Requirements

Onions require full sun for at least six hours a day to grow properly. Planting onions in a shady area can result in slower growth and smaller bulbs.

Spacing Considerations

When planting onion sets, space them about 4-6 inches (10-15 cm) apart in rows that are 12-18 inches (30-45 cm) apart. This spacing allows the plants to grow and develop properly without overcrowding. Crowded onion plants can result in smaller bulbs and increased risk of disease.

Following these seasonal considerations can help ensure a successful onion set crop and a bountiful harvest.

Planting Onion Sets: Step-by-Step Guide

Once you’ve chosen the perfect location and prepared the soil, it’s time to plant your onion sets. Follow these step-by-step instructions to ensure a successful crop:

  1. Prepare the Soil: Rake the soil to create a level planting surface.
  2. Dig Planting Holes: Use a hoe or trowel to create holes about 1-2 inches deep and 4-6 inches apart. Rows should be spaced 12-18 inches apart.
  3. Place Onion Sets: Place each onion set gently in the planting hole, with the pointed end facing up. The tops of the sets should be level with the soil surface.
  4. Backfill the Holes: Using your hands or a gardening tool, backfill the holes with soil and firm it down gently to secure the onion sets in place.
  5. Water Thoroughly: Depending on the climate and soil moisture levels, onion sets may need regular watering to support growth. Water thoroughly after planting and continue to water as needed.
  6. Add Mulch: Adding a layer of mulch around the newly planted onion sets can help regulate soil moisture and temperature, which is especially important in hot or dry climates.
  7. Monitor for Pests and Diseases: Keep an eye out for pests and diseases that may affect your onion sets. Early detection and treatment can help prevent a larger issue down the line.

It’s important to handle onion sets with care, as they can be easily damaged during planting. Try to keep the tops and roots intact, and avoid planting onion sets that are soft or discolored. In general, onion sets should be planted in the spring, as soon as the ground is workable.

Storing Onion Sets

If for some reason you’re unable to plant your onion sets right away, it’s important to store them properly to prevent them from drying out or rotting. Store onion sets in a cool, dry, well-ventilated area until you’re ready to plant them.

Caring for Onion Sets: Watering, Fertilizing, and Weed Control

Once onion sets are planted, they require proper care to ensure healthy growth and maximum yield. This section will cover important aspects of onion set care, including watering, fertilizing, and weed control.

Watering Onion Sets

Onion sets require regular watering to ensure healthy growth. However, overwatering can lead to disease and rotting. As a general rule, onion sets should receive about 1 inch of water per week, whether through rainfall or irrigation. It’s important to water deeply, so the moisture reaches the roots, rather than just wetting the surface. To prevent disease, avoid getting the leaves wet and water in the morning when the temperature is cooler. Once the leaves start to turn yellow and the tops begin to fall over, reduce watering to allow the onions to dry out before harvesting.

Fertilizing Onion Sets

Onion sets require regular fertilization to ensure optimal growth and development. Before planting, mix a balanced fertilizer into the soil to provide the necessary nutrients. Once the onion sets begin to grow, side dress with nitrogen-rich fertilizer every two to three weeks. Be sure not to over-fertilize, as this can lead to excessive foliage growth and small bulbs. A good rule of thumb is to use about one tablespoon of fertilizer per plant.

Weed Control for Onion Sets

Weeds can compete with onion sets for nutrients and water, leading to reduced growth and yield. To prevent weed growth, apply a layer of organic mulch around the onion sets. This will also help to retain moisture in the soil. Hand-weeding around the onion sets is also an effective way to control weeds. Avoid using herbicides, as they can damage the onion sets and negatively impact the soil.

Protecting Onion Sets from Pests and Diseases

One of the biggest challenges for onion set growers is protecting their crop from pests and diseases. Here are some tips to help prevent and control common issues:

Pest-Resistant Onion Varieties

Choosing pest-resistant onion varieties is the first step in preventing pest infestations. Look for varieties that are resistant to thrips, onion maggot, and other common pests in your area.

Cultural Practices

Practicing good cultural practices can help prevent pest and disease problems. Keep your onion bed clean and free of weeds, as weeds can harbor pests and diseases. Avoid overwatering or underwatering your plants, as both can stress them and make them more susceptible to pests and disease.

Organic Pest Control Methods

If you do encounter a pest problem, there are many organic pest control methods you can use to control the infestation. Neem oil, insecticidal soap, and pyrethrin sprays are all effective against many common onion pests. You can also use physical barriers like row covers to protect your plants.

Preventing Disease

To prevent onion diseases, make sure you are planting your sets in well-draining soil and rotating your onion crop regularly. Avoid overwatering and overcrowding your plants, as both can create conditions that are perfect for disease development. If you do encounter a disease problem, remove infected plants immediately and destroy them to prevent the disease from spreading to other plants.

Chemical Controls

If you have a severe pest or disease problem that cannot be controlled with organic methods, chemical controls may be necessary. Always read and follow the instructions carefully when using chemical controls, and use them as a last resort.

By following these tips and keeping a watchful eye on your onion sets, you can prevent and control pest and disease problems to ensure a healthy and abundant crop.

Harvesting and Storing Onion Sets: Best Practices

Harvesting onion sets at the right time is crucial to achieve optimal flavor and storage. Use the following tips to ensure that your onions are harvested and stored properly.

Signs of maturity Harvest technique Curing and storage
Yellowing foliage and falling over are signs that the onion sets are ready to be harvested. Using a spading fork or shovel, gently loosen the soil around the onions. Pull up the onions and let them dry in the sun for a few hours. After drying, remove the roots and the dead foliage. Leave the onions to cure in a warm, dry, and well-ventilated area for several weeks. Once the outer skins are dry and papery, trim the necks and roots and store the onions in a cool, dark, and dry place.

When storing onions, keep in mind the following:

  • Store onions away from potatoes and other vegetables that release moisture or gases that can cause onions to spoil.
  • Do not store onions with fruits that give off ethylene gas, such as apples and pears. Ethylene gas can speed up the spoilage of onions.
  • If storing onions in a mesh bag, hang the bag in a cool and dry place to allow for air circulation.
  • Check stored onions regularly for any signs of sprouting, softening, or rotting, and remove any bad onions to prevent the spread of spoilage.

By following these best practices for harvesting and storing onion sets, you can enjoy the fruits of your labor for months to come.

Common Onion Set Growing Problems and Solutions

Despite following the essential tips for growing onion sets, issues may still arise during the growth period. Here are some common problems you may encounter and solutions to help overcome them:

Inconsistent Bulb Size

If your onion sets are producing bulbs of varying sizes, it could be due to irregular watering or a lack of nutrients in the soil. Ensure that you are watering your onion sets regularly and applying fertilizer as needed. You may also want to consider spacing your sets further apart to allow for more growth.


If your onion sets are bolting, or producing seed heads before the bulb has fully matured, it may be due to a period of cold weather or other environmental stressors. To prevent bolting, plant your onion sets at the appropriate time for your climate and ensure they are receiving adequate sunlight and moisture.

Yellowing Leaves

If the leaves of your onion plants are turning yellow, it could be a sign of overwatering or a lack of nutrients in the soil. Make sure your soil is well-draining and that you are not overwatering your plants. Consider adding some fertilizer to the soil to give your onion sets the nutrients they need.


If your onion sets are overcrowded or growing too close together, you may need to thin them out to allow for better growth. Carefully remove some of the smaller sets, leaving plenty of space between the remaining sets.


Onion sets can be susceptible to a variety of diseases, including onion smut, white rot, and onion downy mildew. To prevent disease, make sure your soil is well-draining and does not become waterlogged. Consider using disease-resistant onion varieties, practicing crop rotation, and avoiding overhead watering.


Common pests that can affect onion sets include onion maggots, thrips, and aphids. To prevent pest damage, use insecticidal soap or neem oil, plant your onion sets at the appropriate time, and practice good garden hygiene by removing any plant debris or weeds that may attract pests.

Frequently Asked Questions about Growing Onion Sets

Growing onion sets can be a rewarding experience, but it’s common to have questions along the way. We’ve compiled a list of frequently asked questions to help guide you through the process.

How do I store onion sets before planting?

Onion sets should be kept cool and dry before planting. Store them in a well-ventilated area, away from direct sunlight and moisture. Ideally, they should be stored at a temperature between 35-40°F.

What is the optimal planting depth for onion sets?

Onion sets should be planted at a depth of 1 to 1.5 inches. It’s important not to plant them too deeply, as this can result in stunted growth.

How do I prevent my onion sets from bolting?

To prevent onion sets from bolting, it’s important to plant them at the right time and provide them with adequate water and nutrients. Avoid planting them too early in the season when temperatures are still cool, and make sure they receive consistent moisture.

Can I grow onion sets in containers?

Yes, onion sets can be grown in containers as long as the container is at least 8 inches deep and has good drainage. Use a well-draining potting mix and make sure to water them regularly.

How do I know when to harvest my onion sets?

Onion sets are usually ready to harvest when the tops begin to turn yellow and fall over. Carefully lift them out of the soil using a garden fork, being careful not to damage the bulbs.

How do I cure and store my onion sets after harvest?

To cure and store onion sets, allow them to dry in a warm, dry place for several weeks. Once they’re completely dry, trim the roots and tops and store them in a cool, dry place. They can be stored in a mesh bag or tied together with string and hung up.

How do I control onion maggots in my garden?

To control onion maggots, practice good crop rotation and avoid planting onions in the same spot year after year. You can also use row covers to protect your plants from adult flies. If you do notice maggots in your onions, remove and destroy the affected plants.

Can I grow onions from seed instead of onion sets?

Yes, onions can be grown from seed. However, they can take longer to mature and may not produce as well as onion sets. If you do choose to grow onions from seed, start them indoors several weeks before the last frost date in your area.