Onion Seeds: The Why, What and How of Growing Onions from Seeds in Your Garden

Onions are a cool-weather crop and can be started from seed in early spring. Sow onion seeds in a sunny location in well-drained soil. Cover the seeds with 1/4 inch of soil and water well. Thin the plants to 8 inches apart when they are 2 inches tall. Onions require well-drained soil and do not perform well in wet soil. Fertilize with a balanced fertilizer weekly.

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Onion Seeds

Onions are members of the genus Allium, including garlic, leeks, and shallots. They are believed to have originated in Central Asia and then spread worldwide. Onions are used in many different dishes, both savory and sweet. They can be eaten fresh, cooked, or pickled.

Onion Seeds
Onion Seeds

How do you start an onion seed?

Onions are relatively easy to grow and can be grown from seed or starter plants. If you grow onions from seed, you will need to plant them in late winter or early spring, before the last frost. The seeds can be planted directly in the ground or pots or flats. The seeds should be spaced about an inch apart, and the soil should be well-drained and will grow best in temperate climates.

How to get Onion Seeds

If you grow onions from starter plants, you can purchase them at your local garden center. Plant them in late spring, after the last frost. Space the plants about 12 inches apart, and water them regularly. Onions will grow best in full sun. 

Onions can be harvested at different stages of development, depending on how you plan to use them. If you are harvesting them for fresh use, you can pick them when they are young and tender. If you are harvesting them for cooking, you can wait until they are more mature. Finally, if you are harvesting them for pickling, you will want to wait until they are very mature.

Gardening with onions is great because they are versatile, they can be used in many different dishes, and they are a great source of vitamins and minerals.

Growing onions from seed enable you to cultivate various forms, flavors, sizes, and colors. Here are some suggestions for choosing appropriate types for your growing area and starting onions from seed indoors under lights.

Onions are a kitchen staple that contributes taste to various meals throughout the year. Each year, one of my garden goals is to plant enough onions to make enough sauces and salsas for family meals, canned sauces and salsas, and winter storage.

Onions can be cultivated from seeds, transplants, or sets. Onion transplants are supplied in bunches and can be purchased online or at a garden center location near you. Onion sets are immature bulbs planted the previous year and are readily available in the spring at garden centers and nurseries.

As a child, I recall planting onion sets each spring when my mom “did the gardening.” When I began my garden, I carried on the habit of purchasing scoops of onion sets and planting them in the spring. In general, I did not have much success growing onions from sets. Some were duds that failed to sprout, while others bolted before developing into giant bulbs. The onions that did germinate from sets were relatively tiny and did not store well. I was also dissatisfied with the limited selection of onion sets, typically labeled yellow, white, and red.

onion seeds
onions bulbs

Growing onions from seed require a lot of patience. 

Sowing indoors in January or February under growing lights and transplanting them to the garden in early spring is the only way I can grow onions from seed in my zone 5 gardens and have them mature. If you reside in a more southern climate, you can plant onion seeds in late summer or early fall, and they will germinate when the weather warms.

Choose Your Onion Seeds Carefully: Because onion seeds are perishable, purchase just those you will use within one or two years. If you’re keeping onions for winter usage, choose types with a reputation for long-term storage. Additionally, choose types that are appropriate for your growing environment. Onions are classified according to their day length: short-day, day-neutral, and long-day.

Short-day onions thrive in zones 7 and higher, where the moderate climate enables them to grow throughout the fall and winter months and be harvested in March, April, and May. When sunlight is increased to 10-12 hours each day, short-day onions begin to bulb (look yours up here). Red Burgundy, Vidalia, and Red Creole are all common short-day onions.

In virtually all climates, day-neutral or intermediate-day onions can be produced. However, when daylight hours rise to 12-14 hours, day-neutral onions begin to bulb. Candy and Cabernet are two common day-neutral onions.

In the North, where plant hardiness zones 6 and below apply, we grow long-day onions. They are sown under lights early in the season and moved to the garden in the spring, giving them ample time to mature before becoming bulbs. When the length of the day increases to 14-16 hours, long-day onions begin to bulb (look yours up here). Paterson, White Sweet Spanish, and Ailsa Craig are examples of long-day onions.

onion seedlings
onions-seedlings

How to grow onions from seed indoors

Sow onion seeds indoors eight to ten weeks before the last frost date in your area. I plant onion seedlings in discarded berry containers. The containers are approximately 4 inches deep and have numerous drainage holes.

1. Fill your containers halfway with pre-moistened seed beginning mix, evenly sprinkle the seeds on top of the soil, spray with water, cover with 1/8-inch seed starting mix, and gently press down to ensure that the seeds are in contact with the moist soil.

2. Label the containers, place them in a seed flat or other watertight container, cover them with a humidity dome, and lay them on a heat mat or in a warm location between 70 and 75°F (21-24°C).

3. Once the seeds have sprouted, remove the humidity dome and set them in a cool spot under lights.

4. Maintain an even moisture level in the soil: Water with diluted fish emulsion or compost tea every two weeks. Trim the tops of the onion seedlings with scissors to maintain them around 3-inches tall. This prevents the pots from becoming top-heavy and ensures that nutrients are directed toward the roots rather than the foliage. 

The trimmings can be used as topping for soups, salads, and pizza.

Prepare the Onion Seedlings for Hardening Off:

Onions are frost resistant and can withstand cooler spring conditions. Begin hardening off onion transplants approximately four weeks before the final anticipated frost date. Keep an eye out for frigid conditions in your area. While onions can tolerate chilly temperatures, their young seedlings are susceptible to frost and freeze damage. 

How to Prepare Transplants for Hardening Off.

Hardening off is acclimating plants to the outside environment to thrive in the sunlight, cool nights, and less frequent watering. Begin hardening off the seedlings in a covered spot for a few hours the first day and gradually increase the time until they are outside overnight.

How to plant onion seeds Outdoors.

Choose a site for growth that receives full sun or at least six hours of direct sunshine per day. Onions thrive in fertile, loose soil that drains well. Add completed compost to the area to add nutrients and organic matter to aid drainage. Before planting, incorporate an all-purpose organic fertilizer into the soil, such as Espoma Plant Tone.

spring onion
spring onion blooming

What month do you plant onion seeds?

The best time to plant onion seeds are in the months of September, October, and November in the Northern Hemisphere, and it will be spring in the Southern Hemisphere). This is because onions need a long, cold period of dormancy before sprouting and growing. Therefore, the ideal temperature for planting onion seeds is around 55-70 degrees Fahrenheit.

How long does it take to grow onion from seed?

It takes about 3-4 months for onion seeds to sprout. Onion seeds need a lot of light and warmth to grow. They need to be kept moist at all times but not too wet, or they will rot and die.

Transplantation 

1. carefully remove the seedlings from the container by gently squeezing the plastic, placing your palm over the seedlings, turning the container upside down, and gently shaking.

2. When the root ball is removed from the container, it frequently breaks apart. The roots will firmly anchor to the soil if the onions are sown more densely. Tease the onion seedlings gently apart for planting one at a time to prevent the roots from drying out.

3. Transplant the seedlings that have been separated. Depending on the kind, 3 to 4 inches apart. I transfer onion seedlings with a fork or other tiny utensil. I carefully push the earth forward, insert the onion seedling, then softly push the soil back. There will be no patting or tamping in.

4. Once the seedlings have been transplanted, gently moisten the bed. Onions have a shallow root system and require frequent watering to maintain a consistent moisture level in the soil. Keep the bed weeded to prevent the onions from competing for nutrients and resources.

Onions can be collected as green onions or allowed to mature completely. When the tops of the onions flop over, the growth cycle is complete. At this time, stop watering and wait for a dry day to harvest. Then, harvest, cure, and store for the winter at the appropriate time. 

ornamental onion flower
ornamental onion flower

Summary and General tips to Cultivate Onions

Germination Period

When seeds are started indoors, they germinate in 4-10 days.

When Should Transplantation Be Performed?

Plant outside shortly before the last frost.

Requirements for Spacing

When transplanting your seedlings, leave a minimum of 6 inches between them. Plant onion seedlings in an area of your garden that is least weedy; onion seedlings are small and struggle to compete with weeds.

Particular Considerations

Make a deep trench in your soil, at least 4 inches deep, before the final frost. To facilitate transplanting, water this furrow before planting your seedlings.

Growing onions from seed problems

Numerous bacterial, fungal, and viral illnesses can all harm onion growth. Insect pests can also be a concern in different locations of the United States to varying degrees. Crops in storage can be affected by diseases and fungi such as Fusarium basal rot, white rot, and Botrytis neck rot. Crop rotation can assist in preventing the spread of certain diseases.

Consuming Onions

Onions have an infinite number of culinary applications and are indispensable for enhancing savory foods. Among their many uses, onions are roasted, fried, pickled, sautéed, and incorporated into a variety of other cuisines. Especially for salads, pasta, and soups, bunching onions are ideal. Onion jam or compote is an excellent method to use up a surplus of red onions, which do not store as well as white or yellow onions.

Storing and Preserving

After harvesting, dry onions for two to three weeks in a warm, shaded location. When the onions are paper-dry on the outside, trim the tops and roots and lightly brush away any remaining soil before keeping them in a cold, dry area. Arrange them in a single layer or use mesh bags to hang them. Always handle onions with extreme caution; even the tiniest injury will promote rot. Onions that have been adequately cured will keep for 6–8 months in a root cellar or cool basement.

The Best Way to Preserve Onion Seeds

Onion seeds are generally not difficult to produce or collect, but keep in mind that they are a biennial crop, meaning they seed every two years.

onion plant stamens

Cycle of Life

Biennial

Isolation Distance That Is Recommended?

When preserving onion seeds, keep varieties at least 800 feet apart and up to 12 miles apart. To make onion seed, select as many perfect onions as you can spare for seed production and keep them in a cold, dry, dark spot over the winter. They should be replanted in early spring at the same bulb depth and spacing as when harvested.

Population Sizes That Are Recommended

Save seeds from at least five plants to ensure healthy seeds. To ensure long-term variety, preserve seeds from between 20 and 50 plants.

Assessing the Maturity of Seeds

During the second season’s late summer, keep an eye out for blossoms and eventually seed heads. Allow sufficient time for the seed heads to dry. After that, most of the blossoms will have dried, and the seeds will begin to fall naturally.

When to Harvest and How to Harvest

Once the bulbs have matured, the bulb onion plants’ tops naturally fall over. When half of the tops in planting have fallen over, lift all of the bulbs and store the pulled plants in a warm, dry location (out of direct sunshine) to cure.

Harvesting Seeds

Once the plants have bloomed, and the seed heads have begun to dry, collect the seed heads in a paper bag. The majority of the seeds will fall out naturally; shake the bag to release the remaining seeds.

Cleaning and Preparation

Disentangle the seeds from the stalks and other components of the seed head. Allow a few days for the seeds to air-dry before storing them in a cool, dry place.

Storage and Resilience

Onion seeds remain viable for two years when stored in a cold, dark, and dry location.

Conclusion

If you are looking for a way to save money on your grocery bill, then learning to grow onions from seed is a great way to do it. Onions are a staple in most kitchens, and they can be expensive to buy at the grocery store. By growing your onions, you can save a lot of money, and you will always have a fresh supply of onions to use in your cooking.

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Michael is an author and entrepreneur that specializes in content production and marketing. I love helping authors and entrepreneurs succeed. My life experiences have given me a unique worldview, which I've used to write compelling material for my audience. Thank You