Handyman: The A-Z Guide to How To Grow Onions From Seed

There are a few things most of us who grow our own food find as satisfying as growing our family’s meal. You are in control of your food supply and gaining the valuable skill of self-reliance as you grow vegetables from seed to fruit-bearing plant. Onions are among the most rewarding crops to start from seed, providing home gardeners with an inexpensive way to produce larger quantities and varieties that are not commonly available in stores as onion sets.

Growing onion seeds requires patience and planning, but the rewards are great. You save money (and get better flavor), and you can find specialty types, such as the enormous’ Ailsa Craig’ or sweet ‘Walla Walla.’ Plus, you get the satisfaction of nurturing these versatile vegetables from baby sprout to your dinner plate.

This complete guide will cover everything you need to know about planting onion seeds – choosing the right varieties for your region, sowing seeds, caring for young plants, and preparing your crop for year-long storage.

Why are Onion Seeds Not Sets

There are several reasons to consider growing onion seeds instead of using onion sets. Firstly, you’ll find a much greater selection of onion seeds available for purchase compared to the limited options traditionally offered as sets. Specialty types such as ‘Blush,’ ‘Apache,’ and ‘Cortland’ are seldom sold in sets but are easy to find as seeds.

Cost-effectiveness is another significant benefit. One packet of onion seeds can yield hundreds more plants just as inexpensively as a small bag of onion sets. This means starting onions from seed can be extra appealing for gardeners who want to grow in volume or on a budget.

Growing onions from onion seeds also gives you more control over the health of your plants right from the start. Purchased sets can transmit disease (or, at the very least, will not benefit the performance of your crop if they come into contact with an unsuitable storage method). Seeds allow you to begin with clean, healthy plants and grow them in your own controlled environment.

Understanding Onion Types

Understanding the three major types of onions and the kind that is suitable for your growing area is vital to know before choosing onion seeds to grow. This categorization is based on the daylight needs for bulb formation, not simply flavor preferences.

Long-Day Onions

Onion varieties that are long-day need at least 14 hours of sunlight to grow bulbs. These are some commonly grown kinds for the north, where the days of summer are longest. If you live in the northern half of the U.S. (roughly north of a line from San Francisco to Washington D.C.), long-day onions are for you.

Common long-day cultivars are ‘Bradley,’ ‘Cortland,’ and ‘Delgado.’ They also store very well and are 90-110 days till maturity. Sow them in late winter or early spring for a late summer crop.

Short-Day Onions

Short-day onions start to bulb when they receive 10-12 hours of daylight. These types are well-suited for the south and warmer climates (mostly in zone 7 and higher). Growing temperature and day length influence the quantity of leaves and thus the size of onion bulbs.

‘Alison’ and ‘Granex’ are popular short-day types. In warm-winter areas, plant these onions in the fall for a late-spring crop. Early spring planting in cooler zones can be fine, but expect smaller bulbs and a harvest only about 75 days long.

Day-Neutral Onions

Day-neutral onions develop bulbs in 12-14 hours of daylight, making them suitable for intermediate zones 5-6. These types provide some options for gardeners in intermediate climates and can yield sweet, mild onions.

‘Expression’ is a widely adapted day-neutral variety that does well from transplants in the north. These onions are generally around 110 days to maturity and store for short- to mid-term.

Starting Onion Seeds Indoors

Success growing onions from onion seeds starts indoors. Timing is essential — you should sow onion seeds 10-16 weeks before your last anticipated frost date. The longer time frame (16 weeks) is popular with seasoned gardeners who want to make sure their seed-grown onions get as large as the sets they buy.

Materials and Timing

Collect these tools and materials for growing onions from onion seeds:

• High-quality seed starting mix
• feature a drainage hole (shallow cells are best)
• Plant labels
• Spray bottle for gentle watering
• Grow lights or a bright south-facing window

The date to start onion seeds indoors will depend on where you live. Late February to early March is suitable for most of us northern gardeners. Gardeners who have a long season ahead can start seeds in late fall for winter growing.

Sowing Technique of Onion Seeds

Fill your containers almost to the top with seed starting mix. Make two shallow trenches, 1/4 inch deep, spanning the width of the container. Sow onion seeds thickly in the furrows — don’t worry about exact temporization or spacing for now, since you will transplant them in clusters later.

Lightly cover the onion seeds with additional starting mix, and label each container with your variety. Keep the soil consistently moist with a spray bottle to avoid seeds from washing around. Put the containers in a warm spot (70-75°F) for better germination.

Germinating Onion Seeds

It can take 10-14 days for onion seeds to germinate, leaving plenty of room for improvement. When germination has started, place the containers into bright light — either beneath grow lights or in a sunny window. Strive to maintain the soil evenly moist, never waterlogged.

As the seedlings grow, they can get very tall and fall over. When the green shoots are about 6 inches tall, clip them back to four inches with clean scissors. This stimulates energy to develop roots and bulbs instead of excessive top growth.

Transplanting Onion Seedlings

Onions are also quite cold-hardy, and you can transplant them straight into the garden many weeks before your final frost date. This early planting also means they have a longer growing season, which is particularly crucial for types that require a long season to make large bulbs.

Preparing the Garden Bed

Pick a well-drained, sunny location for your onion sets. Onions are best in rich, friable, organic matter-filled soil. Incorporate aged manure or compost into the planting mix at the site before transplanting.

Build furrows or planting holes 6 inches apart in rows. (Vary the spacing depending on your taste and available space.)Enough air flows on all sides to keep bulbs dry (essential for long-term maintenance).

Transplanting Process

Begin hardening off your seedlings about a week by progressively exposing them to outside environments before planting. Start by spending an hour or two outside, then gradually increase your time to spend all day there.

Transplant by carefully removing seedlings from their containers and dividing them into four groups. This is the method of clustering that expert growers have used for years, which makes maintenance EASY, and often results in bigger total harvests. Plant each cluster with the roots swathed and the small bulb set about ¼ inch below soil level.

Water newly transplanted plants well, and cover them with a mulch layer to keep water in and keep weeds out. This helps retain water. In case of the chance for continued freezing temps, mulch also insulates young plants.

Caring for Growing Onion Plants

Onions thrive with constant care, watering, fertilizer application, and weed control through the growing season. Onions have a fibrous root system, are very susceptible to competition (to weeds) and moisture stress.

Watering Requirements

During the growing season, ensure that the soil remains consistently moist, but do not let it stand in water. Onions produce the best with 1 inch of water a week, including rain. Deep, less frequent watering promotes deep root growth compared to more frequent shallow watering.

While forming bulbs (usually mid-summer), consistent moisture is essential. Lack of water at this phase may cause bulbs to be too small or onions to bolt.

Fertilizing Strategies

Onions do best with even feeding throughout their growth. Fertilize with a well-balanced fertilizer at planting, then side-dress nitrogen one or two times during periods of active growth.

Cease the fertilization regimen around 6-8 weeks before the anticipated harvest. Over-applying late-season nitrogen may delay bulb maturity and storage potential.

Weed Management

Weeds are very competitive with onions because of their shallow root systems, and compete for water and nutrients; therefore, weed control is essential for maximizing yield. Shallow cultivation should be practised frequently when the weeds are small, to prevent the roots of the onions from being disturbed.

Mulch around onion plants to help discourage weeds and retain soil moisture. Organic mulches, like straw or shredded leaves, are beneficial for gardening and landscaping. There are effective options for gardening. They are excellent, but either way, keep the mulch that retreated a little from the base of the plant. Each plant helps avoid pest and disease problems.

Managing Pests and Diseases

Although onions are relatively pest-free, there are a few pests that can harm your crops. Awareness of these pitfalls and following preventative steps are critical to a productive harvest.

Common Pests

Onion thrips are tiny insects that feed on various plants. Onion leaves, causing silvery streaks and occasionally decreased bulb size. Maintain close watch on crops and use reflective mulches or beneficials for management.

The root, especially in cool, wet weather, may be riddled by the onion maggot. Rotation of crops and sanitation are beneficial for preventing these infestations. Light covers in the early growth stage can protect young plants/saplings from the insult of unprotected conditions.

Disease Prevention

Onions can also be susceptible to fungal diseases such as downy mildew and purple blotch, particularly in moist weather. Make sure there is good air movement around plants and refrain from watering overhead if you can help it.

Poorly draining soils or prolonged wet periods can lead to root rot. To avoid this, improve soil drainage and refrain from overwatering.

Rotate crops, never planting onions in the same place within three years. That breaks up disease cycles and keeps soil healthy.

Harvesting and Storing Your Onions

It is essential to know when and how to harvest onions so you can get the best results and storage life from them. By harvesting and curing properly, you can enjoy your homegrown onions far into winter.

When to Harvest

Most onions should be harvested as soon as their green leaves start to turn yellow and fall over on their own. This is normal for spring-planted onions, which are typically harvested in late summer. I do not wait for all the tops to turn over—harvest when about 50-75% have fallen on their own.

You can promote the process by gently bending over any of the remaining upright tops about a week before harvest. This sends a signal to the plant that it has stopped growing, and the natural curing process begins.

Curing Process

Once harvested, onions must be cured appropriately if they are to develop their protective outer skins and attain maximum storage life. Remove the roots or tops, but don’t brush off excess soil yet.

Lay onions in a single layer in a warm, dry, well-ventilated location for 2 to 3 weeks. Good air flow is necessary — don’t cure in enclosed containers or a damp basement.

Storage Tips

When cured adequately, onions can be kept for months. Trim roots and tops to about 1 inch, and store in mesh bags, baskets, or braided strings in a cool, dry, dark place.

The storage ability of the various types varies. Long-day onions generally store better than short-day ones, and some cultivars such as ‘Bradley’ and ‘Cortland’ can last 6–8 months if adequately cured and stored.

Popular Onion Varieties to Try

Growing varieties of onions will allow you to find out the taste and set of qualities that are suitable for your taste and conditions. Here are a few great options for growing onions from seed:

20 Best Onion Varieties to Grow From Seed. These onion varieties are some of the best to grow from onion seeds.

• Alison is a good, round Granex-type onion for southeastern gardens. Matures at the mid-season, with sweet, mild bulbs for fresh eating.
• ‘Apache‘ offers something unique: a red bunching onion that can be harvested early as purple scallions or left to mature into eye-catching spring onions with bright colour.
• ‘Blush‘ has an eye-catching pinkish-brown skin with light purple rings. This Long Day storage hybrid has good storage potential and a unique visual appeal.
• Bradley Large Long Day Storage Onion – 175 Seeds. List price: $8.39. Bradley is a long-day onion that produces huge onions with dark pink skin. It has high yields and stores very well.
• ‘Cortland‘ is an all-star both as a garden-fresh eating onion and for storage. They’re perfectly round, firm to the touch, with a tough skin, and they store extremely well.
• Dawson (6-7) is a Spanish variety with excellent heat tolerance, making it great for hot summer climates. It has excellent storage and strong disease resistance.

Frequently Asked Questions

What is the best time to sow onion seed?

Sow onion seeds indoors 10-16 weeks before your last frost date. For most gardeners north of the Equator, that means starting seeds in late February to early March. In warm climates, you might sow seeds in autumn for a winter crop.

How deep should I plant onion seeds into the ground?

Sow onion seeds approximately 1/4 inch deep in a hydroponic seed starting mix. Lightly cover with more soil mix, and keep evenly moist until germination, which takes around 10-14 days.

Is it safe to plant onion seeds directly in the garden?

Yes, you can plant onions from seed in areas with longer growing seasons. But planting indoors means you have more control over growing conditions, and bigger bulbs at harvest time are generally the reward.

When to harvest onions? How can I tell when seed heads should be snipped off of onion plants?

If the onions flower in their first year, cut off/remove the flowering heads as soon as possible. They don’t keep long and should be used fresh. Collect seeds from onions that flowered during their second year of growth following a winter in the soil.

Red onion seeds vs. onion Seeds?

Red onion seeds produce onions with reddish-purple outer skins and rings from top to bottom throughout the bulb. They are planted and grown in the same way as other onions, but they provide color and a subtly different flavor to dishes.

Your Path to Onion Self-Sufficiency

Starting onions from seed enables growing the broadest range of varieties, some unavailable as sets, and it’s also exceptional value for your gardening buck. From the first thrill of watching spiky little green shoots poke up to the final joy of pulling pounds and pounds of homegrown onions out of your garden, there are rewards in planting these that have nothing to do with dinner.

Learn the methods in this guide—from when to start seeds to how to store onions—that will give you the skills to ensure consistent onion growing success. Keep in mind that each growing year is a learning experience, and even seasoned garden veterans never stop tweaking things to fit their particular situation and taste better.

Take small steps at first, starting with a few varieties suitable for your climate zone, before proceeding further with growing onions once you get the hang of it. With adequate planning and care, you’ll quickly discover the unmatched flavour and satisfaction that comes from increasing these culinary workhorses from seed.