Growing Onions for the Home Garden: Your First Crop From Sets to Storage

Onions are one of the easiest vegetables to grow and one of the most rewarding. They take up very little space, they resist most pests, and a successful harvest will feed your table for months.

You do not need a big garden to grow onions. A few good feet in a raised bed or a patch in the ground is enough. You do not need fancy equipment or special soil. You just need to know which type of onion to plant and when to plant it.

That second part is the real secret. Most onion failures come from planting the wrong variety for your region. Get that right and the rest is straightforward.

Why Onions Deserve a Spot in Your Garden

Onions earn their place for three simple reasons.

They store for a long time. A properly cured and stored onion will keep for eight to twelve months in a cool, dry place. That means one spring planting can supply you through the following winter. No freezing, no canning, no special equipment.

They are low maintenance once established. After the first few weeks of weeding and watering, onions are remarkably self-sufficient. They do not attract many serious pests, and their natural sulfur compounds keep most insects away.

They do not take much room. A row of onions twenty feet long will produce dozens of bulbs. You can squeeze them into tight spaces that would be useless for squash or tomatoes. They also work well alongside other crops as a companion plant, especially near carrots and tomatoes.

You can grow several types in one garden. Yellow onions store the longest. Red onions are best for fresh eating and slicing. Sweet onions like Walla Walla or Vidalia have a mild flavor that is hard to beat raw. Planting a mix gives you variety through the season and flexibility in the kitchen.

The One Decision That Determines Everything: Day Length

This is the most important thing to understand about growing onions. Onions form bulbs in response to day length. They are photoperiodic plants, which means the number of daylight hours triggers the bulb to start swelling. If you plant the wrong type for your latitude, your onions will either never bulb or bolt to seed before they ever get a chance to form a real bulb.

There are three categories.

Short-day onions need about 10 to 12 hours of daylight to start bulbing. They are best suited for gardens in the southern United States, roughly below 36 degrees north latitude. They mature early and are ideal if you live in a warm winter climate.

Long-day onions need 14 to 16 hours of daylight. These are grown in the northern United States, above 40 degrees north latitude. If you plant a long-day onion in the South, it will never get long enough days to trigger bulbing and you will end up with tiny scallion-sized onions.

Intermediate-day onions need 12 to 14 hours of daylight. These work in the middle ground, roughly between 36 and 40 degrees north latitude. Louisville, Tennessee sits at about 35.5 degrees north, which puts it right on the border between intermediate and short-day territory. In Zone 7a, intermediate-day onions are usually the safest choice.

You can find this information on the seed packet or the onion set label. If the package does not specify, ask at the nursery. It is worth five minutes of questions now to avoid a whole season of small onions.

Popular intermediate-day varieties include Texas Early Grey Star, Red Burgundy, and Ails Craig. Popular short-day varieties include Texas Early Granex, Southern Belle, and Red Candy Apple. Popular long-day varieties include Idaho Yellow Onion, Thompson, and Southport Red.

How to Start: Sets, Transplants, or Seeds

You have three ways to get onions into the ground. Each has trade-offs.

Onion sets are small, dormant bulbs that were grown the year before and dried for storage. They are the easiest option for beginners. You just plant them and they go to work immediately. The downside is limited variety selection and a slightly higher risk of bolting (going to seed before bulbing), especially if you plant them too early or if they were stored poorly. Buy sets that are pencil-width or smaller. Anything thicker than a pencil is more likely to bolt.

Transplants are young onion plants started by a nursery and sold in bundles. They give you a head start on the season without the patience required for seeds. Selection is better than sets but not as wide as seeds. Transplants are my personal recommendation for most home gardeners. They are easy to plant, give good establishment, and have a lower bolt rate than sets.

Seeds give you the widest variety selection and the lowest bolt risk, since you control exactly when the plants go in the ground. The catch is timing. Onions started from seed need 10 to 12 weeks indoors before you can transplant them outside. That means starting onion seeds in late winter, which is inconvenient if you do not have a sunny windowsill or grow lights. Seeds also take longer to reach a harvestable size.

If you are growing onions for the first time, go with sets or transplants. You will get a faster result and it will be easier to judge success.

When and Where to Plant

Onions are a cool-season crop. They do best when planted early in the spring, while the air is still crisp and the soil is cooling off from winter.

Timing: Plant onion sets or transplants 2 to 4 weeks before your last expected spring frost date. In Zone 7a, that usually means mid to late February for sets and early March for transplants. The soil temperature should be at least 45 degrees Fahrenheit. Onions can tolerate a light frost once they are established, which is one reason early planting works so well.

If starting from seed: Sow seeds indoors 10 to 12 weeks before your last frost date. In Zone 7a, that is late January to early February. Sow them shallow, about a quarter inch deep, in a well-draining seed mix. Keep the soil evenly moist. Seedlings will be ready to transplant when they are about the thickness of a pencil and 6 to 8 inches tall.

Site selection: Onions need full sun, which means at least 6 to 8 hours of direct sunlight per day. They grow best in loose, well-drained soil with a pH between 6.0 and 6.8. If your soil is heavy clay, amend it with compost before planting. Onions will not bulb properly in compacted or waterlogged ground.

Spacing: Plant sets or transplants about 4 to 6 inches apart in rows that are 12 to 18 inches apart. Plant them just deep enough that the tips are barely covered, about half an inch. Do not plant them deeper. Burying an onion set too deep is a common mistake that results in small or misshapen bulbs.

Fertilizing: Onions are moderate feeders. Work compost or aged manure into the soil before planting. Then apply a side dressing of nitrogen-rich fertilizer when the plants first show green growth in spring. A light application again four to six weeks later will support bulb development. Do not over-fertilize, or you will get lots of green tops and small bulbs.

Growing Through the Season

Once your onions are in the ground, the work is mostly about keeping them weeded and steadily moist.

Weeding: Onions have shallow roots and do not compete well with weeds, especially in the first six weeks. Keep the area around them clean. A shallow layer of mulch helps suppress weeds and keeps soil moisture even. Pull weeds by hand or use a shallow hoe. Do not dig deeply around onion roots.

Watering: Onions need about one inch of water per week, whether from rain or irrigation. They are shallow-rooted and do not store much water, so consistent moisture matters more than heavy watering. Water deeply and less frequently rather than light sprinkles every day. Cut back watering once the bulbs begin to swell and the tops start to fall over, as too much water at that stage can encourage rot.

Watching for trouble: The most common onion problems are thrips (tiny insects that feed on the leaves), onion maggot (white maggots that bore into bulbs), and fungal diseases like downy mildew. Thrips are usually manageable by keeping the garden weed-free and using row covers early in the season. Onion maggot can be reduced by rotating crops and not planting onions in the same bed year after year. Downy mildew thrives in cool, wet conditions, so good air circulation and avoiding overhead watering help.

For most home gardeners, onions are far less trouble than tomatoes, squash, or potatoes. As long as you keep them weeded and evenly moist, they will mostly take care of themselves.

Harvesting and Curing

Onions tell you when they are ready. You do not need a calendar or a ruler. Watch the plants.

When the top halves of the onion plants naturally turn yellow and fall over, the bulbs are done growing. About 70 to 80 percent of your plants falling over is your signal to start preparing for harvest. If you wait too long and all the tops have collapsed, the bulbs may split or rot in the ground.

How to harvest: Choose a dry day. Gently loosen the soil around each bulb with a garden fork and lift. Brush off excess soil. Do not wash them. Leave the tops and roots attached for now.

Curing: Lay the onions in a single layer in a warm, dry, well-ventilated spot out of direct sunlight. A garage, shed, or covered porch works well. You can also hang them in breathable mesh bags or old pantyhose. Let them cure for two to three weeks. They are done when the outer skins are completely dry and papery, the roots are shriveled, and the necks are tight and closed.

Do not skip curing. Freshly dug onions have high moisture content and will not store well. Proper curing seals the outer layers and gives you months of storage life.

Storing Your Onions

After curing, trim the tops to about one inch and gently brush away any loose outer skins. Do not remove the papery layers that are still attached. Inspect each bulb and set aside any that feel soft, show green spots, or have damaged skin. Those should be eaten first.

Store the good bulbs in a cool, dry, dark place with good air circulation. A basement, root cellar, or unheated garage works well. Ideal storage temperature is 35 to 50 degrees Fahrenheit with about 65 to 70 percent humidity.

Good storage options include:

• Mesh bags or net bags hung in a cool, airy space
• Wicker baskets stacked in a single layer
• Old pantyhose with one onion tied per section, hung from a rafter
• Wooden crates with the slats allowing airflow

Do not store onions in sealed plastic bags or airtight containers. They will sweat and rot. Do not store them near potatoes. Potatoes release moisture and gases that cause onions to spoil faster.

When stored properly, yellow and red onions will last eight to twelve months. Sweet onions have a higher water content and will not store as long, usually six to eight weeks at best. Use those first.

Getting Started

If you have never grown onions, this is a good year to try. Pick up a packet of intermediate-day onion sets or a bundle of transplants from a garden center in late February or early March. Plant them in a sunny spot with loose, well-amended soil. Keep them weeded and evenly moist through the spring. In early July, watch for the tops to fall over. Cure them for a few weeks and put them in a cool, dry place.

By November, you will be reaching into a storage bin and pulling out a homegrown onion to chop for dinner. That is not a big accomplishment on paper. But it is one of the most satisfying things you can do in a garden, and it only takes a few square feet to make it happen.

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— C. Steward 🥕