Master How to Grow Onions from Transplants with Our Guide

If you’re looking to grow onions in your garden, you might be wondering how to get started. While growing onions from seeds is a popular option, there’s another way that may offer even better results: transplanting onion seedlings. In this article, we’ll show you how to grow onions from transplants and share valuable tips to ensure your success.

Why Choose Transplants for Growing Onions?

Growing onions from transplants is a popular and effective method for many gardeners. Transplanting onion seedlings, rather than starting from seed, offers several advantages that can increase the chances of a successful harvest.

Here are a few reasons why you should choose transplants for growing onions:

Advantages of Using Transplants
Transplants save time
Provide uniform growth
Increase the chances of a successful harvest

When starting from seed, it can take several weeks for onions to germinate, and then several more weeks for the seedlings to reach a transplantable size. Using transplants, on the other hand, can cut down the wait time and get you to harvest sooner.

Transplants also ensure more uniform growth, meaning that all of your onions will mature at a similar rate and be of a similar size. This is particularly helpful for gardeners looking to sell their onions or those who want to ensure a consistent supply for their kitchen.

Finally, using transplants can increase your chances of a successful harvest. When starting from seed, there is always the risk of poor germination or the seedlings failing to thrive. Using transplants from a reputable source can help alleviate these risks and give your onions a better chance of reaching maturity.

Why not just use onion sets?

Some gardeners may wonder why they should bother with transplants when onion sets are also an option. Onion sets are small bulbs that are usually planted in the spring and can produce mature onions in just a few months.

While onion sets can be a convenient option for some gardeners, they can also come with their own set of challenges. For example, onion sets can be more prone to disease and insect problems, and they may not produce onions of as high a quality as those grown from transplants. Additionally, onion sets are often grown from varieties that may not be as well-suited to your specific growing conditions.

Overall, using transplants for growing onions can be an excellent way to save time, ensure uniform growth, and increase your chances of a successful harvest.

Selecting and Preparing Transplants

Choosing the right onion seedlings is crucial for a successful transplant. It’s important to select seedlings that are healthy, disease-free, and have a well-established root system.

When purchasing onion transplants, look for seedlings that are at least 6 inches tall with firm, white roots. Avoid any seedlings with yellow or droopy leaves, as these are signs of stress or disease.

Before planting, prepare the soil by adding a layer of organic compost or well-rotted manure. Onions prefer a slightly acidic soil pH between 6.0 and 6.8. If your soil is too acidic, add lime to raise the pH or sulfur to lower it.

Spacing Transplants

The spacing between transplant onion plants is essential for their growth and bulb development. Space the plants 4-6 inches apart in rows that are 12-18 inches apart. It is crucial to have ample space between the plants, and avoid overcrowding to reduce the risk of disease and improve bulb size.

If you’re unsure about the optimum spacing, use a ruler or measuring tape to mark out evenly spaced holes in your garden bed.

Transplanting Onions in the Garden

Transplanting onions is easy and can be done after the last frost in your area. Make sure the soil is well-drained and has a pH level between 6.0 and 7.0. Onions prefer full sun and fertile soil that is rich in organic matter.

Before transplanting, make sure to water your onion transplants and loosen the soil. Using a garden trowel, dig a hole that is about 2 inches deep and wide enough to accommodate the root system of the transplant. Space your onion transplants about 4-6 inches apart and make sure they are planted at the same depth as their original container.

Carefully remove the onion transplant from its container. If the roots are tightly bound, gently tease them apart with your fingers. Place the onion transplant in the hole and fill it with soil, pressing down firmly to remove any air pockets. Water your newly transplanted onions thoroughly to help them settle in.

Tips for Transplanting Onions in the Garden

  • Water your onion transplants a few hours before transplanting them to reduce stress on their roots.
  • If the weather is hot and dry, transplant onions in the evening or on an overcast day to reduce water loss through transpiration.
  • When transplanting, handle your onions gently to avoid bruising or breaking their delicate foliage.
  • Apply a layer of mulch around your transplanted onions to conserve moisture and suppress weed growth.
  • Consider purchasing onion transplants from a reputable source to ensure they are disease-free and healthy.

With proper care and attention, your transplanted onions will grow strong and healthy. Keep an eye out for any issues, such as pests or disease, and address them promptly to ensure a successful harvest.

Essential Care for Transplanted Onion Plants

Proper care is essential for transplanted onion plants to grow successfully. Here are some tips to help ensure healthy growth:


Onions require consistent moisture to grow properly, but it’s important not to overwater them. Water deeply, ensuring the soil is moist to a depth of at least 6 inches. Avoid overhead watering, as this can lead to disease and fungal growth. Instead, water at the base of the plants, using a soaker hose or drip irrigation system.


Onions need a steady supply of nutrients to produce healthy foliage and bulbs. Apply a balanced fertilizer every few weeks, following the manufacturer’s instructions. Avoid fertilizers high in nitrogen, as this can lead to excessive foliage growth and smaller bulbs.

Weed Control

Weeds can compete with onions for water and nutrients, stunting their growth. Keep the area around the onion plants weed-free, either by hand weeding or using a hoe.

Pest and Disease Control

Common pests that can affect onions include onion maggots, thrips, and aphids. To prevent infestations, monitor plants regularly and address any issues promptly. Additionally, onions are susceptible to fungal diseases such as white rot and downy mildew. To prevent fungal growth, avoid overhead watering and ensure proper soil drainage.

By following these guidelines for caring for transplanted onion plants, you can help ensure successful growth and a bountiful harvest.

Monitoring and Maintaining Onion Transplants

Once your transplanted onions have started to grow, it’s important to monitor and maintain them to ensure healthy growth and a successful harvest. Here are some tips to help you along the way.

Watering Techniques

Onions need regular watering to thrive, especially during hot, dry spells. Watering should be done deeply and infrequently to encourage deep root growth. Aim to give your onions around 1 inch of water per week, but adjust according to weather conditions.

Be careful not to overwater, as this can lead to root rot and other fungal diseases. Ensure that the soil has good drainage and avoid watering during the hottest part of the day. Watering early in the morning or late in the evening is best.


Onions require regular fertilization to promote healthy growth. Before planting, work in a slow-release fertilizer or compost into the soil to provide nutrients over time. Once your onions have started to grow, you can also use a nitrogen-rich fertilizer to encourage leaf growth. Avoid using high-nitrogen fertilizers once the onions have started to bulb, as this can stunt growth.

Weed Control

Weed control is important for onions, as they have shallow roots and can be easily outcompeted by weeds. Mulching around your plants can help to suppress weeds and retain moisture. Regular weeding by hand or using a hoe is also effective, but be careful not to damage the onion roots.

Pest and Disease Control

Onions are susceptible to a range of pests and diseases, including thrips, onion maggots, and downy mildew. Regularly inspect your plants for signs of damage or disease and take action as needed. Insecticidal soap or neem oil can be effective for controlling pests, while proper spacing and good ventilation can help prevent fungal diseases.

Nutrient Deficiencies

Onions are especially vulnerable to nutrient deficiencies, especially if the soil is lacking in key minerals. Common deficiencies include nitrogen, phosphorus, and potassium. If you notice signs of yellowing leaves or stunted growth, it may be a sign that your onions need additional nutrients. A balanced fertilizer or compost can help to address these issues.

Harvesting and Storing Onions

Once your onions have matured, it’s time to harvest them. The timing of the harvest depends on the variety of onion you’re growing, but generally, you’ll want to harvest them when the tops start to yellow and fall over.

To harvest, gently pull the onions out of the soil by the tops. Lay them in the sun to cure for a few days. This allows the outer layer to dry and protect the onion during storage. After curing, remove any excess dirt and trim the tops down to about an inch.

When storing onions, it’s important to keep them dry, cool, and well-ventilated. You can store them in a mesh bag or a crate with slatted sides to promote airflow. Keep them in a dark place, like a pantry or basement, and check them regularly for any signs of spoilage.

Pro tip:

Store onions away from potatoes, as the gases they emit can cause both to spoil more quickly.

Troubleshooting Common Onion Transplanting Issues

While growing onions from transplants is generally straightforward and easy, like any garden project, issues may arise. Here are some common onion transplanting issues and tips for troubleshooting them:

Stunted Growth

If your transplanted onions seem to be growing at a slower pace than usual, several factors could be at play. First, check that the soil is not too compacted or waterlogged, as this can limit root growth. Additionally, ensure that the onions are receiving enough sunlight and nutrients. If necessary, consider feeding with a balanced fertilizer or adjusting the amount of water they receive.

Yellowing Leaves

Yellowing leaves can be a sign of a nutrient deficiency, particularly nitrogen. If your onions are displaying yellowing leaves, try feeding with a nitrogen-rich fertilizer to see if this helps. Alternatively, it could be a sign of too much water or soil that is too compacted, leading to poor drainage.

Bulb Rot

Bulb rot is a fungal infection that can affect transplanted onions, causing the bulbs to become soft and decayed. To prevent this issue, ensure that the soil is well-draining and that the onions are spaced out enough to allow for good airflow. Additionally, avoid overwatering and consider using a fungicide if the infection is severe.

Insect Pests

Common insect pests that can affect transplanted onions include thrips, onion maggots, and cutworms. To prevent these pests, consider using an insecticide or planting onions alongside companion plants that repel insects. Additionally, avoid planting in soil that has previously been used for onions or other alliums, as this can attract pests.

By troubleshooting these common issues and taking preventative measures, you can ensure that your transplanted onions remain healthy and productive throughout the growing season.

Companion Planting with Onions

Companion planting is the practice of planting different crops together to benefit each other or to deter pests. When it comes to onions, there are some plants that can help improve onion growth and flavor, and others that should be avoided.

Plants that Benefit Onions

Onions can benefit from being planted with certain plants, including:

Companion Plant Benefit
Carrots Carrots and onions grow well together and can help repel pests that affect both crops.
Lettuce Lettuce is a good companion for onions as it provides cover and keeps the soil cool and moist, which is beneficial for onion growth.
Tomatoes Tomatoes and onions are a classic pairing in recipes, but they also benefit from being planted together. Tomatoes can help repel pests that affect onions and vice versa.

Plants to Avoid Planting with Onions

There are also some plants that should be avoided when companion planting with onions, including:

  • Beans: Beans and onions can both attract onion maggots, which can damage the crop.
  • Peas: Similar to beans, peas can attract onion maggots and should be avoided.
  • Chives: While chives are in the same family as onions, they can compete for nutrients and water if planted too closely together.

By carefully planning your onion garden and choosing the right companion plants, you can help ensure a healthy and successful harvest.

Tips for Success with Onion Transplants

While growing onions from transplants can be a straightforward process, it requires some attention to detail to ensure successful growth. Here are some additional tips to keep in mind:

1. Mulching

Applying mulch around your transplanted onion seedlings can help retain moisture in the soil and suppress weed growth. Consider using organic materials such as straw or compost to promote healthy growth.

2. Temperature Management

Onions prefer cooler temperatures, ideally between 55-75°F. To manage temperature, consider shading your transplanted onion plants during hot summer afternoons, or planting them in a shaded area of your garden.

3. Sunlight Exposure

Onions require sunlight exposure for healthy growth. Make sure to plant your transplanted onion seedlings in an area that receives at least six hours of full sun per day.

4. Good Airflow

Proper airflow around your onion plants can help prevent fungal diseases. Make sure to provide adequate spacing between plants to allow for good airflow, and avoid overcrowding them.

5. Consistent Watering

Onions require consistent moisture to grow, but be careful not to overwater them as this can lead to root rot. Consider watering your transplanted onion seedlings deeply once or twice per week, depending on weather conditions.

6. Fertilization

Onions require a balanced amount of nutrients to grow properly. Consider fertilizing your transplanted onion plants with a slow-release organic fertilizer rich in nitrogen and phosphorus.

By following these tips, you can help ensure the success of your onion transplanting endeavors and enjoy a bountiful harvest!

Commonly Asked Questions about Growing Onions from Transplants

Here are some commonly asked questions about growing onions from transplants:

1. When is the best time to transplant onion seedlings?

The best time to transplant onion seedlings depends on your location and climate. In general, wait until the soil has warmed up and there is no more risk of frost. This is usually in early spring to early summer.

2. How deep should I transplant the onion seedlings?

When transplanting onion seedlings, make sure you bury them deep enough so that only the top of the leaves stick out of the soil. Typically, you should plant the seedlings about 1-2 inches deep.

3. How often should I water my transplanted onions?

Water your transplanted onions regularly, but avoid overwatering them. The frequency of watering will depend on the weather and the soil conditions. Make sure the soil is moist, but not waterlogged.

4. How can I prevent my onions from bolting?

Bolting is when the onion plant produces a flower stalk prematurely. To prevent this, make sure your onions are planted in well-draining soil, they are watered consistently, and they are not overcrowded. Additionally, avoid planting onions too late in the season as this can also cause premature bolting.

5. How can I tell when my onions are ready to harvest?

When the leaves of the onion plant start to turn yellow and fall over, this is a sign that the onions are ready to be harvested. Carefully dig them up and allow them to dry out in a warm, dry place for a few days before storing.

6. Can I plant other vegetables near my transplanted onions?

Yes, onions are great companion plants for many vegetables including tomatoes, peppers, and lettuce. However, avoid planting onions near beans or peas as they can stunt their growth.

7. How long do onions grown from transplants last in storage?

If stored properly, onions grown from transplants can last up to 8 months in storage. Make sure the onions are dry and stored in a cool, dark place with good ventilation.

8. Do I need to fertilize my transplanted onions?

Yes, onions do need fertilizer to grow properly. Fertilize your onions with a balanced fertilizer once a month throughout their growing season.

9. Can I grow onions from transplants in containers?

Yes, onions can be grown from transplants in containers. Make sure you use a container that is at least 6 inches deep and has good drainage. Also, make sure the container is in a sunny location and the soil is kept moist.

10. Why are my transplanted onion seedlings not growing?

There could be several reasons why your transplanted onion seedlings are not growing. Make sure they are planted in well-draining soil, they are not overcrowded, and they are receiving enough water and sunlight. Additionally, check for any signs of pests or disease.


Transplanting onion seedlings can be a great way to grow onions with ease and success. By following the tips and advice in this guide, you can grow healthy, delicious onions that will add flavor and nutrition to your meals. If you have any additional questions or concerns, feel free to reach out to us for assistance!


Here are some of the frequently asked questions about growing onions from transplants:

1. What is the best time to transplant onion seedlings?

The ideal time to transplant onion seedlings is when they are at least 8 weeks old and have grown to about 6 inches in height. This usually falls in early to mid-spring, depending on your location and climate.

2. How deep should I plant the onion seedlings?

Make sure to plant the onion seedlings with the base of their leaves level with the soil surface, with the roots extending into the soil below. The depth of the planting hole does not need to be very deep.

3. How often should I water my transplanted onions?

While onion plants prefer dry soils between watering, it is crucial to ensure consistent moisture levels to prevent stress. Water the transplanted onions at least once a week, depending on the weather and soil conditions. Avoid overwatering as it can lead to fungal diseases.

4. How can I prevent onion pests and diseases?

Onion pests and diseases can cause significant damage to transplanted onions. To prevent this issue, make sure to plant healthy seedlings and keep the garden and surrounding area clean by removing any debris. You can also use organic pesticides or companion planting to deter pests and diseases.

5. Can I use transplants for all types of onions?

Yes, you can use transplants for all types of onions, including red, white, yellow, and shallots. However, make sure to choose the appropriate onion variety for your region and climate.