How To Plant Onion Plants [ Full Guide ]

Onions are a versatile and essential ingredient in a wide variety of culinary dishes, and growing your own onions can be a rewarding and enjoyable experience. Planting onion plants requires careful consideration of the variety, soil conditions, and the planting process to ensure a successful harvest. In this guide, we will explore the step-by-step process of planting onion plants, from selecting the right variety to preparing the planting area and caring for the growing onions.

Quick Answer: How To Plant Onion Plants

  1. Choose the right variety: Select an onion plant variety that is well-suited to your climate and intended use, whether it’s for green onions, bulb onions, or storage onions.

  2. Prepare the planting area: Ensure the planting site receives full sun, has well-drained soil, and is free from weeds and debris.

  3. Soil requirements: Test the soil pH and fertility, and amend the soil as needed to provide optimal growing conditions for the onions.

  4. Planting process: Plant the onion sets or transplants at the appropriate depth and spacing, ensuring they are well-watered and mulched to retain moisture.

  5. Care and maintenance: Provide regular watering, weed control, and fertilization to encourage healthy onion growth.

  6. Harvesting: Monitor the onions as they grow and harvest them when they have reached the desired size and maturity.

By following these steps, you can successfully plant and cultivate your own onions, providing a fresh and flavorful addition to your homegrown produce.

Choosing The Right Onion Plant Variety

Before you begin the process of planting onion plants, it’s important to select the right variety that suits your growing conditions and desired use. There are several types of onions to consider, each with its unique characteristics:

Bulb Onions

Bulb onions are the most common type of onions, forming the large, round bulbs that are harvested for culinary use. These onions can be further divided into short-day, long-day, and intermediate-day varieties, which are suited to different growing regions based on the length of daylight hours.

  • Short-day onions: These onions are suited to regions with milder winters and are often grown in the southern United States. They require 10-12 hours of daylight to form bulbs, making them ideal for planting in the fall and harvesting in the spring or early summer.

  • Long-day onions: Long-day onions are better suited to northern regions with longer daylight hours. They require 14-16 hours of daylight to bulb, making them suitable for planting in the spring and harvesting in the late summer or fall.

  • Intermediate-day onions: These onions fall between short-day and long-day varieties and are suitable for regions with moderate day length variations. They typically require 12-14 hours of daylight to bulb and can be planted in a broader range of climates.

Green Onions

Green onions, also known as scallions or spring onions, are harvested before the bulb fully forms. They are prized for their mild flavor and are commonly used in salads, stir-fries, and garnishes. When choosing a variety for green onions, consider ones that are known for their tender and flavorful tops.

Storage Onions

Storage onions are harvested after the bulbs have fully matured and dried, allowing them to be stored for an extended period. These onions are ideal for long-term storage and culinary use throughout the year.

When selecting the right onion variety, consider your local climate, the length of daylight hours, and the intended use of the onions. Look for varieties that are well-suited to your region and provide the flavor and storage characteristics you desire.

Preparing The Planting Area

Once you have selected the appropriate onion variety for your growing conditions, it’s crucial to prepare the planting area to provide the best environment for the onion plants to thrive.


Onion plants require full sun, which means they should receive at least 6-8 hours of direct sunlight each day. Choose a planting site that is not shaded by trees, buildings, or other structures to ensure the onions receive adequate sunlight to support their growth and bulb development.

Soil Drainage

Good soil drainage is essential for successful onion cultivation. Onions are prone to rot if they are sitting in waterlogged soil, so it’s crucial to select a well-drained planting site. Avoid areas that are prone to flooding or where water tends to collect after rainfall.

Soil Preparation

Clear the planting area of any weeds, rocks, or debris that could interfere with the onion planting. Use a garden fork or tiller to loosen the soil to a depth of at least 6-8 inches, breaking up any compacted areas and creating a loose, friable planting bed.

Soil Requirements For Onion Plants

Onions thrive in fertile, well-drained soil with a slightly acidic to neutral pH level. Conduct a soil test to determine the pH and fertility of the soil in the planting area. Most onions prefer a pH level between 6.0 and 7.0. If the pH level is too low (acidic) or too high (alkaline), it can affect the availability of essential nutrients for the onions.

Soil Amendment

Based on the results of the soil test, amend the soil as needed to create an optimal growing environment for the onion plants. Common soil amendments for improving soil fertility and pH include:

  • Organic Matter: Add well-rotted compost or aged manure to improve soil structure and provide essential nutrients for the onions.

  • Lime: To raise the pH of acidic soil, incorporate agricultural lime according to the recommendations of the soil test. This helps neutralize the acidity and create a more suitable growing environment for the onions.

  • Sulfur: If the soil is too alkaline, sulfur can be added to lower the pH and make the soil more acidic. Again, follow the recommendations of the soil test to determine the appropriate amount of sulfur needed.

Mix the soil amendments thoroughly into the planting bed to ensure they are well-integrated and distributed throughout the soil. This process not only provides the necessary nutrients but also improves the soil structure and drainage, setting the stage for successful onion growth.

Planting Onion Plants

Once the planting area is prepared and the soil is amended, it’s time to plant the onion sets or transplants according to the specific requirements of your chosen variety.

Choosing Onion Sets Or Transplants

Onion plants can be grown from seeds, sets (small onion bulbs), or transplants. Sets and transplants are popular options for home gardeners because they offer a head start in the growing process and can reduce the time to harvest compared to starting from seeds.

Planting Time

The ideal time to plant onion sets or transplants largely depends on the onion variety and your local climate. Typically, onion sets are planted in the early spring, while onion transplants are often set out in late winter or early spring, a few weeks before the last expected frost date in your area.

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Planting Depth And Spacing

When planting onion sets or transplants, adhere to the following guidelines to ensure successful growth:

  • Depth: Plant the sets or transplants approximately 1 inch deep in the soil. If planting in rows, space the sets or transplants 4-6 inches apart within the row, allowing for proper bulb development.

  • Row Spacing: For traditional row planting, space the rows 12-18 inches apart to provide adequate room for the onions to grow and facilitate cultural practices such as watering, mulching, and weeding.

Watering And Mulching

After planting the onion sets or transplants, water the area thoroughly to settle the soil around the roots and provide essential moisture for the developing plants. Apply a layer of organic mulch, such as straw or shredded leaves, around the onion plants to help retain soil moisture, suppress weeds, and maintain a consistent soil temperature.

Care And Maintenance

Once the onion plants are established, they require regular care and maintenance to encourage healthy growth and bulb development. Here are some essential care practices for successful onion cultivation:

  1. Watering: Onions need consistent moisture to thrive, especially during the bulb-forming stage. Water the plants deeply once a week if there is no rainfall, ensuring that the soil is evenly moist but not waterlogged.

  2. Weed Control: Keep the area around the onion plants free from weeds, which can compete for nutrients and water. Mulching helps in suppressing weeds, but occasional hand-weeding may be necessary to maintain a weed-free planting bed.

  3. Fertilization: Side-dress the onions with a balanced fertilizer when they have established their root systems and are actively growing. Apply the fertilizer according to the manufacturer’s recommendations, taking care not to let it come into direct contact with the onion foliage.

  4. Pest and Disease Management: Monitor the onion plants for signs of pests, such as thrips, onion maggots, and diseases such as downy mildew or botrytis. Implement appropriate measures, such as insecticidal soaps or beneficial insect release, to manage pest infestations and maintain plant health.

  5. Thinning and Harvesting Green Onions: If you are growing green onions, thin them as they grow to allow space for the remaining plants to develop into larger bulbs. Harvest green onions by trimming the tops as needed, leaving the roots and a portion of the bulb in the ground to produce additional growth.

Successfully planting onion plants requires careful consideration of the variety, soil preparation, and planting process. By choosing the right onion variety, preparing the planting area, and providing appropriate care, you can cultivate flavorful, homegrown onions for culinary use. Remember to monitor the onions as they grow, provide essential care, and harvest them at the appropriate time to enjoy the fruits of your labor. With proper attention to detail and best practices, you can experience the satisfaction of producing your own fresh and flavorful onions.

Spacing Onion Plants

Onions are a versatile and flavorful vegetable that can be grown from sets, transplants, or seeds. When properly planted and cared for, onions can be continuously harvested throughout the growing season.

Proper spacing is crucial when planting onion plants as it allows them to develop healthy bulbs without competing for nutrients and sunlight. The spacing requirements may vary depending on the variety of onion you are growing, so always refer to the seed packet or plant label for specific guidelines.

  1. Determining the spacing: On average, onion plants should be spaced 4 to 6 inches apart in rows. However, if you are growing larger onion varieties, the spacing should increase to 6 to 8 inches.
  2. Preparing the soil: Choose a well-draining site with full sun exposure for planting onions. Before planting, loosen the soil to a depth of at least 12 inches and remove any weeds or debris.
  3. Creating furrows: Use a garden hoe or shovel to create furrows in the prepared soil. The furrows should be about 1/2 inch deep and spaced according to the desired spacing between onion plants.
  4. Planting the onion plants: Place each onion plant in a furrow, ensuring that the roots are spread out. Gently press the soil around the plant to secure it in place. Repeat this process for each onion plant, maintaining the recommended spacing between them.

Proper spacing allows the onion plants to grow and develop without crowding each other. It also facilitates air circulation, reducing the risk of disease and mold growth.

Watering Onion Plants

Onions require consistent and adequate moisture to grow healthy and keep their leaves firm and upright. Proper watering practices can contribute significantly to the overall health and productivity of your onion plants. Here are some guidelines for watering onion plants effectively:

  1. Watering frequency: Onions prefer regular watering, especially during dry periods. Aim to provide about 1 inch of water per week. However, be cautious not to overwater the plants, as this can lead to rotting and disease.
  2. Watering technique: To prevent wetting the foliage excessively, it is best to water onions at the soil level. Drip irrigation or a soaker hose can be used to ensure the water goes directly to the base of the plants.
  3. Timing of watering: Water your onion plants early in the morning to allow the foliage to dry off during the day, as wet leaves can be susceptible to fungal diseases. Avoid overhead watering, particularly in the evening, as this increases the risk of fungal infections.
  4. Monitoring soil moisture: Regularly check the moisture level of the soil by inserting your finger or a moisture meter into the ground. If the soil feels dry at a depth of 1 to 2 inches, it is time to water the onions.

By providing consistent moisture to your onion plants while avoiding overwatering or wetting the foliage, you can ensure their healthy growth and reduce the risk of diseases.

Mulching Onion Plants

Mulching is an essential practice for onion plants, as it helps conserve moisture, suppresses weed growth, and provides insulation to the bulbs against temperature fluctuations. Here are the steps to effectively mulch onion plants:

  1. Choosing mulch: Organic mulches such as straw, shredded leaves, or grass clippings are excellent options for mulching onion plants. These materials break down over time, enriching the soil with organic matter.
  2. Applying mulch: Once your onion plants have reached a height of about 2 to 3 inches, apply a 2 to 3-inch layer of mulch around the base of the plants. Ensure that the mulch is not directly touching the stems to prevent rotting.
  3. Adjusting mulch thickness: As the onion plants grow, you can gradually increase the mulch thickness to 4 to 6 inches. This allows for better insulation and weed suppression while retaining moisture in the soil.
  4. Mulching maintenance: Regularly check the mulch and remove any moldy or decaying sections. Also, replenish the mulch layer as necessary to maintain the desired thickness.
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Mulching not only conserves moisture and suppresses weeds but also helps regulate soil temperature, which is crucial for the growth and development of onion bulbs.

Fertilizing Onion Plants

Providing the proper nutrients to onion plants is key to achieving healthy and robust growth. Here are some guidelines for fertilizing onion plants:

  1. Soil preparation: Before planting your onion plants, incorporate organic matter such as compost or well-rotted manure into the soil. This will enrich the soil with essential nutrients and improve its overall fertility.
  2. Preplant fertilizer: Prior to planting, apply a balanced slow-release fertilizer according to the package instructions. This will provide the necessary nutrients for the initial growth of your onion plants.
  3. Side-dressing during growth: Approximately four weeks after planting, when the onion plants have established a healthy root system, you can begin side-dressing with a nitrogen-rich fertilizer. Apply the fertilizer alongside the rows, about 2 to 3 inches from the plants, and gently work it into the soil.
  4. Frequency of fertilization: Repeat the side-dressing process every three to four weeks throughout the growing season to ensure a steady supply of nutrients to the onion plants. However, be cautious not to overfertilize, as this may result in excessive foliage growth and smaller bulbs.
  5. Ceasing fertilization: Approximately two to three weeks before harvesting, stop applying nitrogen-rich fertilizers. This allows the onion plants to divert their energy towards bulb development.

By incorporating organic matter into the soil, providing preplant and side-dressing fertilizers, and maintaining a proper fertilization schedule, you can ensure that your onion plants receive the essential nutrients they need for healthy growth and abundant bulb production.

Controlling Pests And Diseases

Despite their resilience, onion plants are prone to certain pests and diseases that can impact their growth and overall health. Taking preventive measures and practicing proper garden hygiene can help minimize these risks. Here are some common pests and diseases that affect onion plants and how to control them:

  1. Onion thrips: These tiny yellow-brown insects feed on onion leaves, causing silver streaks and stunted growth. To control thrips, use row covers or insecticidal soap and regularly wash the leaves using a strong stream of water.
  2. Onion maggots: The larvae of onion flies, onion maggots feed on the roots of onion plants, causing wilting and often death. To prevent infestation, cover the newly planted onion sets with floating row covers and remove any infected plants promptly.
  3. Fungal diseases: Diseases such as onion white rot, downy mildew, and purple blotch can affect onion plants. To minimize the risk of fungal infections, ensure proper air circulation, avoid overhead watering, and promptly remove any infected plants and debris from the garden.
  4. Weed control: Weeds compete with onion plants for nutrients and moisture. Regular weeding and the use of mulch can help suppress weed growth and ensure healthier onion plants.
  5. Crop rotation: To prevent the buildup of pests and diseases in the soil, practice crop rotation by avoiding planting onions in the same spot for consecutive years. Rotate onions with other non-allium crops, such as legumes or brassicas.

By implementing preventive measures such as using row covers, practicing good garden hygiene, and promptly addressing any pest or disease issues, you can help protect your onion plants and maintain their vigor throughout the growing season.

Planting onion plants requires proper spacing, watering, mulching, fertilizing, and pest and disease control. By following these in-depth guidelines, you can ensure the healthy growth and abundant harvest of your onion plants. Remember to check the specific requirements of the onion variety you are growing and make adjustments accordingly. With dedication and care, you can enjoy the satisfaction of growing your own flavorful onions in your garden.

Harvesting Onion Plants

Onion plants are a versatile and essential part of every kitchen garden. With their distinct flavor and aroma, onions are used in countless dishes to enhance the taste and add depth to the flavors. Growing onion plants can be a rewarding experience, as they are relatively easy to cultivate and require minimal maintenance.

Before diving into the planting process, it’s crucial to understand the optimal time to harvest your onion plants. The timing will depend on the type of onion you are growing, as well as your local climate. Onions can be broadly categorized into two types: short-day and long-day onions.

Short-day onions are typically grown in regions with mild winters and are sensitive to the length of daylight they receive. They form bulbs when daylight duration reaches 10-12 hours. These types of onions are generally planted in the fall and harvested in late spring or early summer.

On the other hand, long-day onions are suitable for regions with colder climates and longer daylight hours. They require 14-16 hours of daylight to form bulbs. Long-day onions are usually planted in early spring and harvested in the summer.

To determine if your onions are ready to be harvested, you can observe the tops or "necks" of the plants. When the foliage begins to turn yellow and falls over naturally, it indicates that the onions are mature and ready for harvest. Gently lift the onions from the soil using a garden fork or trowel, being careful not to damage the bulbs. Allow them to dry in a well-ventilated area for a few weeks, until the outer layers are dry and papery.

Storing Onion Bulbs

Once your onion bulbs have dried, it’s time to store them properly to ensure they last for an extended period. Storing onions correctly will help prevent spoilage and keep them fresh for several months. Here are a few essential tips for storing onion bulbs:

  1. Curing: After drying the onions, make sure to remove any excess soil or debris from the bulbs. Trim the foliage down to about an inch above the bulb. This process is known as "curing" and helps the onions develop a protective layer over their outer skin, improving their storage capabilities.

  2. Air Circulation: For storing onions, choose a location that is cool, dry, and well-ventilated. Air circulation is critical in preventing mold and rot. A garage, shed, or basement with good airflow is ideal for storing onions.

  3. Proper Packaging: Store the cured onions in mesh bags, pantyhose, or slatted wooden crates. These containers allow air to circulate around the bulbs, preventing excess moisture buildup. Avoid using plastic bags or containers as they can trap moisture and cause the onions to rot.

  4. Separation: Ensure that the onions are stored in a manner that prevents them from touching each other. This reduces the risk of rot spreading from one onion to another. You can achieve this by placing a layer of newspaper or straw in between the bulbs.

  5. Temperature and Humidity: Onions can be stored at temperatures between 35-45°F (1-7°C) with a humidity level of 65-70%. Avoid storing them in areas prone to extreme temperature fluctuations or high humidity levels, such as the refrigerator.

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By following these guidelines, you can successfully store your onion bulbs for several months, allowing you to enjoy their fresh flavor even when they are out of season.

Propagating Onion Plants

If you want to grow more onion plants without purchasing new sets or seeds, propagating them from onion bulbs is a viable option. This method is known as "onion propagation." Here’s how you can propagate onion plants:

  1. Selecting Bulbs: Choose healthy and robust onion bulbs from your stored collection. It’s essential to select bulbs that are disease-free, firm, and have intact skins. Bulbs that are starting to sprout are ideal for propagation.

  2. Preparing the Bulbs: Before planting the bulbs, trim any remaining foliage down to an inch or so. This will redirect the energy from the foliage to the formation of new roots and shoots.

  3. Planting in Containers: Fill a container with well-draining potting soil or seed starting mix. Make small holes in the soil, spaced about an inch apart, and insert the onion bulbs with the pointed ends facing up. Cover the bulbs with soil, leaving about a quarter inch of the bulb exposed. Water the soil lightly, ensuring it remains moist but not saturated.

  4. Transplanting Outdoors: If you prefer to propagate onion bulbs directly in the ground, select a sunny location with loose soil. Plant the bulbs at a depth of 1-2 inches, spacing them 4-6 inches apart in rows. Ensure that the soil is well-drained and does not become waterlogged.

  5. Maintenance: Keep the soil consistently moist but not overly wet. Onions prefer regular watering, especially during dry periods. Be sure to weed the area around the onion bulbs to avoid competition for nutrients.

  6. Harvesting: Depending on the variety and growing conditions, you can expect to harvest the propagated onion plants within a few months. Monitor the tops of the plants for signs of yellowing and foliage falling over. Once they are ready, carefully lift the bulbs from the soil, just as you would with mature onions.

By following these steps, you can propagate onion plants and expand your garden without the need for purchasing additional sets or seeds. It’s a cost-effective and sustainable method of growing onions.

Common Mistakes To Avoid While Planting Onion Plants

To ensure a successful onion crop, it’s essential to avoid common mistakes that can hinder their growth and development. Here are some common mistakes to avoid while planting onion plants:

  1. Late Planting: Onions have specific planting windows depending on the type and variety. Delaying the planting beyond the optimal time can result in smaller bulbs or failure to form bulbs at all. Ensure that you plant your onions at the right time for your region and onion type.

  2. Improper Spacing: Onions require adequate space to grow and develop properly. Planting them too close together can result in overcrowding, competition for nutrients, and smaller bulbs. It’s recommended to space onion sets or bulbs at least 4-6 inches apart.

  3. Inadequate Soil Preparation: Onions thrive in loose, well-draining soil with a pH level between 6.0-7.5. Before planting, amend the soil by adding organic matter such as compost or well-rotted manure to improve its fertility and drainage. Avoid heavy clay soils or those prone to waterlogging, as they can lead to root rot.

  4. Improper Watering: Onions require consistent moisture throughout their growing season, but overwatering can be detrimental. Avoid saturating the soil and ensure that the plants receive adequate drainage. Mulching the soil around the onions can help retain moisture and prevent weed growth.

  5. Skipping Weed Control: Weeds compete with onion plants for nutrients, sunlight, and water. Regularly remove weeds from the onion bed to prevent stunted growth and maximize bulb development. Mulching can help control weeds and conserve soil moisture.

  6. Neglecting Fertilization: Onions are moderate feeders and benefit from regular fertilizer applications. Apply a balanced fertilizer with a higher nitrogen content, such as 10-10-10, every few weeks during the growing season. Avoid over-fertilization, as this can encourage excessive foliage growth at the expense of bulb development.

  7. Ignoring Pest and Disease Management: Onions are susceptible to various pests and diseases, including onion thrips, onion maggots, smut, and basal rot. Monitor your plants regularly and take appropriate measures, such as applying organic insecticides or fungal treatments, to manage any infestations or diseases.

By avoiding these common mistakes, you can ensure that your onion plants thrive and produce healthy, flavorful bulbs.


Planting onion plants can be a rewarding experience, providing you with a fresh supply of this versatile kitchen staple. By understanding the optimal time for harvesting, storing the bulbs properly, and propagating new plants, you can enjoy a continuous harvest of onions throughout the year. Remember to avoid common mistakes such as late planting, improper spacing, inadequate soil preparation, and improper watering to maximize your onion plant’s growth and yield. With these tips and guidelines, you’ll be well on your way to successfully growing your own onion plants and enjoying the satisfaction of homegrown produce.


1. What Type Of Soil Is Best For Planting Onion Plants?

Onion plants grow best in loose, well-drained soil that is rich in organic matter. A slightly acidic pH level of 6.0-6.8 is ideal for onion plants.

2. When Is The Best Time To Plant Onion Plants?

Onion plants should be planted in early spring, as soon as the soil is workable and temperatures are consistently above 50°F.

3. How Much Space Should I Leave Between Onion Plants?

Space your onion plants 4-6 inches apart in rows that are 12-18 inches apart. This allows the plants enough room to grow and develop their bulbs without being overcrowded.

4. Can I Grow Onion Plants From Seeds Or Sets?

Onion plants can be grown from either seeds or sets (small bulb-like structures). Sets are easier for beginner gardeners, while seeds can take longer to grow and require more care.

5. How Often Should I Water Onion Plants?

Onion plants need consistent moisture, but not too much water. Provide about 1 inch of water per week, either through rain or irrigation. Avoid creating standing water or soggy soil around the plants, as this can cause root rot.