How To Plant Onion From Seed [ Full Guide ]

Onions are a versatile and essential vegetable that can be easily grown from seed. Planting onions from seed allows you to select from a wide range of varieties, ensuring that you have the perfect onion for your culinary needs. In this guide, you will learn the step-by-step process of planting onion from seed, from selecting the right seeds to preparing the soil and choosing the ideal location.

Onions are a staple ingredient in many dishes, adding flavor and depth to a wide variety of cuisines. Planting onions from seed is a rewarding and cost-effective way to grow your own onions, as it provides the opportunity to choose from a wider selection of varieties than those available as sets or transplants. Growing onions from seed also allows for better control over the growing conditions, resulting in healthier and more flavorful onions.

Quick Answer: How To Plant Onion From Seed

Planting onions from seed can be a rewarding and straightforward process, but it requires attention to detail and some patience. Here’s a quick overview of the steps involved in planting onion from seed:

  1. Selecting the Right Onion Seeds: Choose the variety of onion seeds that best suits your climate and culinary needs.

  2. Preparing the Soil for Planting: Ensure the soil is well-draining, fertile, and free from weeds before planting the onion seeds.

  3. Choosing the Ideal Location for Planting Onions: Select a location with full sun exposure and adequate air circulation for optimal growth.

Now, let’s delve into each of these steps in more detail.

Selecting The Right Onion Seeds

Before you can start planting onion from seed, it’s essential to choose the right variety of onion seeds for your specific needs and growing conditions. There are numerous onion varieties available, each with its own flavor profile, storage capabilities, and adaptation to different climates. When selecting onion seeds, consider the following factors:

  1. Day Length: Onions are categorized into short-day, intermediate-day, and long-day varieties based on the number of daylight hours required to form bulbs. Choose a variety suitable for your location’s day length.

  2. Flavor: Different onion varieties offer unique flavor profiles, ranging from mild and sweet to pungent and savory. Consider the intended use of the onions when selecting a variety.

  3. Storage Qualities: Some onion varieties are better suited for long-term storage than others. If you intend to store your harvested onions, choose a variety known for its excellent storage qualities.

  4. Climate Adaptation: Certain onion varieties perform better in specific climates. Consider the average temperatures and growing conditions in your area when selecting onion seeds.

  5. Disease Resistance: Look for onion varieties with resistance to common diseases in your region to ensure a healthier crop.

Once you have considered these factors, look for a reputable seed supplier or nursery that offers a wide selection of onion seeds. It’s recommended to purchase fresh, high-quality seeds to maximize the chances of successful germination and healthy plant growth.

Preparing The Soil For Planting

Onions thrive in well-draining, fertile soil with a pH level between 6.0 and 7.5. Before planting onion seeds, it’s crucial to prepare the soil to create optimal growing conditions for the onions. Here’s how to prepare the soil for planting onions from seed:

  1. Clear the Area: Begin by clearing the planting area of any debris, rocks, and existing vegetation. This will provide a clean and open space for planting the onion seeds.

  2. Loosen the Soil: Use a garden fork or tiller to loosen the soil to a depth of about 8 to 10 inches. This will improve aeration and drainage, providing a favorable environment for onion root development.

  3. Amend the Soil: Incorporate organic matter such as compost or well-rotted manure into the soil to improve its fertility and structure. This will also help retain moisture and supply essential nutrients to the growing onions.

  4. Soil Testing: Consider conducting a soil test to determine the pH level and nutrient content of the soil. Based on the test results, adjust the pH and nutrient levels as needed to create an optimal growing environment for onions.

  5. Remove Weeds: Take the time to remove any weeds or unwanted vegetation from the planting area. Weeds can compete with the onion seedlings for nutrients and water, so it’s important to start with a weed-free bed.

By taking these steps to prepare the soil, you can create a favorable environment for planting onion seeds and promote healthy onion growth throughout the growing season.

Choosing The Ideal Location For Planting Onions

Selecting the right location for planting onions is crucial for their overall growth and development. Onions thrive in full sun exposure and well-drained soil, so it’s essential to choose a suitable location for planting. Here are some considerations for choosing the ideal location for planting onions:

  1. Sunlight Exposure: Onions require full sun, which means they need at least 6 to 8 hours of direct sunlight per day. Choose a location that receives ample sunlight throughout the day for optimal growth and bulb development.

  2. Air Circulation: Good air circulation helps prevent disease and promotes overall plant health. Avoid planting onions in areas with poor air circulation, such as dense and crowded planting beds.

  3. Soil Drainage: Ensure that the location has well-draining soil to prevent waterlogging, which can lead to root rot and other problems. Avoid low-lying areas that are prone to water accumulation.

  4. Spacing: Consider the spacing requirements for the specific onion variety you are planting. Proper spacing allows for better air circulation and reduces competition among the plants.

  5. Protection from Pests: If possible, select a location that is relatively free from pests and has minimal pest pressure. This can help reduce the risk of pest damage to the onion plants.

By considering these factors when choosing a location for planting onions, you can create an environment that promotes healthy growth and robust onion production.

Planting onions from seed is a rewarding process that begins with selecting the right onion seeds, preparing the soil, and choosing the ideal planting location. By following the steps outlined in this guide, you can set the stage for successful onion cultivation, leading to a bountiful harvest of flavorful and versatile onions. Whether you’re a novice gardener or an experienced grower, planting onions from seed offers a sense of accomplishment and the satisfaction of growing your own produce from start to finish. With careful attention to detail and proper cultivation practices, you can enjoy a thriving onion crop that enhances your culinary creations and provides a source of fresh, homegrown ingredients.

Planting Onion Seeds Indoors

Onions are a versatile and popular vegetable that can be grown from seeds. Planting onions from seed allows you to have a wider variety of onion options compared to using sets or bulbs. It also gives you the opportunity to grow onions that are ideally suited to your climate and taste preferences.

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Planting onion seeds indoors is a great option for gardeners who live in areas with short growing seasons or who want to get a head start on their onion crop. Here’s how you can do it:

  1. Choose the right time: Start planting onion seeds indoors about 8 to 10 weeks before the last expected frost date in your area. This will give the seeds enough time to germinate and develop into seedlings before they are transplanted outdoors.

  2. Select the right container and soil: Use seed trays or small pots that have drainage holes. Fill the containers with a well-draining seed starting mix. Avoid using regular garden soil, as it can become compacted and hinder the growth of the delicate onion seedlings.

  3. Sow the seeds: Moisten the seed starting mix, then sprinkle the onion seeds evenly across the surface. Lightly press the seeds into the soil, ensuring good seed-to-soil contact. Onion seeds are small, so it’s best to pinch a small amount between your fingers and sprinkle them evenly.

  4. Cover and provide warmth: Onion seeds require darkness to germinate, so cover the tray or pots with a plastic dome or plastic wrap. Place the containers in a warm location, ideally around 70 to 75°F (21 to 24°C). You can use a seedling heat mat to provide consistent bottom heat and ensure faster germination.

  5. Maintain moisture: Check the moisture level of the soil regularly and mist with water as needed to keep it consistently moist, but not waterlogged. Avoid overwatering as it can lead to damping off, a fungal disease that can kill the seedlings.

  6. Provide sufficient light: As soon as the onion seeds germinate and the seedlings emerge, remove the plastic covering and place them under grow lights or in a sunny window. Onion seedlings require at least 14 to 16 hours of direct light per day for healthy growth. Adjust the height of the lights to keep them 2 to 3 inches above the plants.

  7. Thin out the seedlings: Once the onion seedlings have grown a few inches tall and have developed their first true leaves, thin them out to provide enough space for each seedling to grow. Trim weaker or overcrowded seedlings at the soil level using sharp scissors, leaving the strongest and healthiest ones.

  8. Fertilize: About 2 weeks after the seedlings have germinated, begin fertilizing them with a diluted liquid fertilizer specifically formulated for seedlings. Follow the manufacturer’s instructions for proper mixing ratios and frequency of application.

Transplanting Onion Seedlings

After the onion seedlings have been growing indoors for 8 to 10 weeks, it’s time to transplant them outdoors. Ideally, this should be done when the soil temperature reaches at least 50°F (10°C). Follow these steps to ensure a successful onion transplant:

  1. Harden off the seedlings: A week before transplanting, gradually expose the onion seedlings to outdoor conditions to acclimatize them. Start by placing them outdoors in a sheltered area for a few hours each day, gradually increasing the time and exposure to direct sunlight.

  2. Choose the planting site: Select a sunny location in your garden with well-draining soil. Onions prefer loose, loamy soil with a pH between 6.0 and 7.5. It should also be free from rocks or heavy clumps of soil that could inhibit the bulb development.

  3. Prepare the soil: Use a garden fork or tiller to loosen the soil to a depth of at least 8 inches (20 cm). Remove any rocks, weeds, or debris from the planting area. Incorporate organic matter like compost or well-rotted manure to improve soil texture and fertility.

  4. Planting depth and spacing: Dig narrow furrows in the prepared soil, about ¼ to ½ inch (0.6 to 1.3 cm) deep. Carefully transplant the onion seedlings into the furrows, spacing them approximately 4 to 6 inches (10 to 15 cm) apart. Gently backfill the furrows, ensuring the base of the seedlings sits level with the soil surface.

  5. Water thoroughly: After transplanting, water the soil immediately and thoroughly to settle it around the roots and remove any air pockets. Onions need consistent moisture to grow properly, so aim to keep the soil evenly moist throughout the growing season. Mulching around the plants can help retain moisture and suppress weed growth.

  6. Provide support: If you live in a windy area, you may need to provide support to the onion seedlings to prevent them from toppling over. Use stakes or small cages to gently support the plants and protect them from strong gusts.

Planting Onion Seeds Outdoors

Planting onion seeds directly outdoors is an option for regions with mild winters and long growing seasons. Here’s how you can do it:

  1. Choose the right time: Wait until the soil temperature reaches at least 50°F (10°C) before sowing onion seeds directly outdoors. In most regions, this will be in early spring. Onions are cool-season crops and can tolerate light frosts, but they will not germinate in cold soil.

  2. Prepare the soil: Select a sunny location in your garden and prepare the soil as described earlier. Remove any weeds, rocks, or debris from the planting area, and incorporate organic matter to improve soil fertility and texture. Rake the soil to create a level surface.

  3. Sow the seeds: Create shallow furrows in the prepared soil, about ¼ to ½ inch (0.6 to 1.3 cm) deep. Space the furrows 4 to 6 inches (10 to 15 cm) apart. Sow the onion seeds evenly along the furrows, ensuring good seed-to-soil contact. Lightly cover the seeds with soil and gently tamp it down.

  4. Water thoroughly: After sowing the onion seeds, water the soil thoroughly to ensure good seed-to-soil contact and promote germination. Continue to water the soil regularly to keep it moist until the seedlings emerge.

  5. Thin out the seedlings: Once the onion seedlings have emerged and grown a few inches tall, thin them out to allow enough space for each plant to develop. Remove the weaker or overcrowded seedlings, leaving the healthiest and strongest ones with sufficient room to grow.

  6. Mulching: Covering the soil around the onion plants with a layer of mulch can help retain moisture, suppress weed growth, and provide insulation. Use organic mulch like straw or compost, and apply it carefully, ensuring that the base of each onion plant is not covered.

  7. Watering: Onions need consistent moisture to develop properly. Monitor the soil moisture regularly and water when the top inch (2.5 cm) of soil feels dry. Water deeply and thoroughly, allowing the water to penetrate the root zone. Avoid overwatering, as it can lead to rotting.

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Watering And Caring For Onion Plants

Proper watering and care are essential for the growth and development of onion plants. Here are some tips to ensure your onions thrive:

  1. Consistent moisture: Onions require consistent moisture, especially during bulb formation. Aim to keep the soil evenly moist but not waterlogged. Irrigate deeply, providing about 1 inch (2.5 cm) of water per week, either through rainfall or manual watering.

  2. Weed control: Keep the onion bed free from weeds, as they can compete with young onion plants for nutrients, water, and sunlight. Regularly remove any weeds that appear within the onion bed, taking care not to disturb the onion roots.

  3. Fertilization: Onions are heavy feeders and benefit from regular fertilization. Apply a balanced vegetable fertilizer, such as a 10-10-10 or 12-12-12 formula, every 3 to 4 weeks throughout the growing season. Follow the manufacturer’s instructions for proper application rates.

  4. Pest control: Onions are relatively resistant to pests and diseases, but there are a few common issues to watch out for. Onion thrips, onion maggots, and onion white rot can affect onion plants. Monitor your plants regularly and take appropriate action if any signs of pests or diseases are detected. This can include using organic insecticides, practicing crop rotation, or removing and destroying affected plants.

  5. Harvesting: The time to harvest onions depends on the variety you are growing. Generally, onions are ready for harvest when the tops start to fall over and turn yellow or brown. Gently dig up the onions from the soil, taking care not to damage the bulbs. Cure the harvested onions by laying them in a cool, dry, and well-ventilated area for a few weeks until the outer dry layers are papery.

Growing onions from seed is a rewarding experience that allows you to have a wider variety of onion options and ensures that they are ideally suited to your taste preferences and climate. Whether you choose to start onion seeds indoors or directly sow them in the garden, following the proper planting and care techniques will help you achieve a bountiful onion harvest. With patience and attention, you can enjoy the taste of freshly grown onions in your favorite recipes straight from your own garden.

Fertilizing Onion Plants

Onions are a versatile and essential ingredient in many culinary dishes. While it is common to find onion sets or bulbs at garden centers, planting onions from seed can be a rewarding and cost-effective option. Growing onions from seed allows for a wider selection of onion varieties and enables you to start the growing process earlier in the season.

Before planting onion seeds, it is important to prepare the soil by incorporating organic matter and ensuring it is well-draining. Onions require a fertile soil with a pH level between 6.0 and 7.0. Conduct a soil test to determine the pH level of your soil and make any necessary adjustments by adding lime to raise the pH or sulfur to lower it.

Onions are heavy feeders, so it is crucial to provide them with proper nutrition. Begin by incorporating a balanced, slow-release fertilizer into the soil before planting. This will provide a steady supply of nutrients to the growing onion plants.

During the growing season, onions benefit from additional fertilizer applications. About four weeks after planting the seeds, side dress the onions with a nitrogen-rich fertilizer. This will promote healthy leaf growth and bulb development. Repeat this process every four to six weeks until the onions are fully grown.

Controlling Pests And Diseases In Onion Plants

Onion plants are susceptible to various pests and diseases that can hinder their growth. By implementing preventive measures and early detection, you can effectively control these problems.

One common pest to look out for is the onion fly. These small flies lay their eggs on the leaves of the onion plants, leading to maggots feeding on the roots. To prevent onion fly infestations, cover the seedbeds with fine mesh netting or floating row covers. These barriers will prevent the flies from reaching the plants.

Another pest that can damage onion plants is the onion thrips. These insects feed on the foliage, resulting in stunted growth and distorted leaves. Regularly inspect your plants for any signs of thrip damage and consider using insecticidal soap or neem oil if infestation occurs.

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Fungal diseases, such as onion downy mildew and onion white rot, can also pose a threat to onion plants. To prevent these diseases, practice crop rotation and avoid planting onions in the same location year after year. Proper spacing between plants will allow for better air circulation and reduce the risk of fungal infections. If signs of disease appear, promptly remove and destroy affected plants to prevent further spread.

Harvesting And Storing Onions

Knowing when to harvest onions is crucial to ensure optimal flavor and storage life. Onions are ready for harvest when their tops start to fall over and dry out. This typically occurs about 100 to 120 days after planting.

To harvest onions, gently loosen the soil around the bulbs using a garden fork or trowel. Carefully lift the onions out of the ground, making sure not to cause any bruising or damage. Once harvested, allow the onions to cure for a week or two in a well-ventilated area with low humidity. This curing process helps to toughen the outer layers and extend the storage life of the onions.

After curing, remove any excess foliage and roots from the onions. Store them in a cool, dry place with good air circulation. Mesh bags or crates are ideal for storage, as they allow for proper ventilation. Onions can typically be stored for several months if kept in the right conditions.

Tips For Successful Onion Planting

  1. Selecting the right onion variety: There are numerous onion varieties available, each with its own flavor profile and growing requirements. Choose a variety that suits your climate and desired taste. Short-day onions are better suited for southern regions, while long-day onions are more suitable for northern regions.

  2. Starting seeds indoors: To get a head start on the growing season, consider starting your onion seeds indoors. Sow the seeds in trays or pots filled with a seed starting mix, about 8-10 weeks before the last frost date in your area. Keep the soil moist and provide sufficient warmth and light for germination.

  3. Planting onion sets: If you prefer to skip the seed starting process, you can also plant onion sets, which are small bulbs. Plant the sets directly in the ground, following the same guidelines for spacing and soil preparation as for seed planting.

  4. Providing adequate water: Onions require consistent moisture, especially during the bulbing stage. Water deeply once or twice a week, ensuring the soil is evenly moist, but not waterlogged. Mulching around the plants can help retain moisture and suppress weed growth.

  5. Thinning and spacing: When the onion seedlings reach a few inches tall, thin them to allow for proper spacing. Onions should be spaced about 4-6 inches apart. Thinning ensures that each onion bulb has enough space to develop fully.

  6. Protecting from frost: Onions are relatively hardy, but young seedlings can be susceptible to frost damage. If you anticipate frost, cover the seedbeds with a layer of straw or a frost blanket to provide protection.

  7. Companion planting: Companion planting onions with certain crops can help repel pests and promote healthier growth. Consider planting onions alongside carrots, lettuce, or spinach, while avoiding planting them alongside beans or peas.


Planting onions from seed can be a satisfying and cost-effective way to grow this essential vegetable in your garden. By following the steps outlined in this guide, from preparing the soil to harvesting and storing the onions, you can successfully cultivate a healthy crop of onions. Remember to provide proper nutrition, monitor for pests and diseases, and implement preventive measures to ensure the best possible outcome. With a little patience and care, you’ll soon be enjoying the flavors of homegrown onions in your favorite dishes.


What Time Of Year Should I Plant Onion Seeds?

Onions can be planted in the early spring, as soon as the ground is workable, or in the fall for overwintering. It is important to avoid planting in the heat of summer, as this can cause them to bolt and produce small bulbs.

How Do I Prepare The Soil For Planting Onion Seeds?

Onions prefer well-drained, fertile soil with a pH level of 6.0-6.8. Begin by tilling the soil to a depth of 8-12 inches and removing any weeds or debris. You can also add compost or organic matter to improve fertility and drainage.

How Should I Plant Onion Seeds?

Onion seeds should be planted 1/4 inch deep in rows, with a spacing of 4-6 inches between seeds. Alternatively, you can sow the seeds in a seed tray and transplant the seedlings later. Keep the soil evenly moist, but not waterlogged, throughout the growing season.

How Long Does It Take For Onion Seeds To Sprout?

Onion seeds can take anywhere from 7-14 days to germinate, depending on the soil temperature. They prefer a temperature range of 60-85°F for optimal germination. Keep in mind that seeds planted in cooler soil may take longer to sprout.

Do I Need To Thin Out The Onion Seedlings?

Yes, it is important to thin out onion seedlings to allow for proper bulb development. When the seedlings are about 4-6 inches tall, thin them to a spacing of 4-6 inches apart. You can use the thinned seedlings in cooking or as green onions.