Onions for the Home Garden: Your First Allium From Set to Storage

Onions are one of the most useful crops you can grow in a home garden. They flavor nearly every meal you cook. They store for months in a cool, dry closet. And they are forgiving enough that a beginner can grow them with just a shovel, a handful of compost, and a willingness to keep the weeds down.

Every onion plant starts small and unimpressive. A pencil-thick green shoot pushes out of the soil and does not look like much. But by late summer, that shoot has swelled into a layered bulb that will carry you through the winter kitchen. The transition from seed to storage onion is one of the most reliable experiences a home gardener can have.

This guide covers the daylength puzzle, whether to buy sets or grow from seed, planting timing for Zone 7a, seasonal care, common problems, harvesting, curing, and storage.

The Daylength Puzzle

The single most confusing thing about growing onions is the daylength requirement. It is not complicated, but getting it wrong means your onions will never bulb. They will just keep growing leaves and stay small forever.

Onions are photoperiodic. That means they monitor the length of daylight and start forming a bulb when the days reach a certain threshold. Different varieties have different thresholds.

Short-day onions bulb when the day reaches about ten to twelve hours of light. These are grown in the deep South, where summer days never get very long. They are planted in the fall in warm climates and harvested in early summer. In Zone 7a, short-day onions planted in spring will not bulb properly because the days get too long before the bulb has a chance to develop.

Long-day onions bulb when the day reaches about fourteen to sixteen hours of light. These are grown in the northern United States and Canada, where summer days are very long. In Zone 7a, long-day onions planted in spring can work, but they may not fully bulb until late summer when the days are longest. If you want your onions ready by mid-August, a long-day variety might finish too late.

Intermediate-day onions, sometimes called day-neutral, bulb when the day reaches about twelve to fourteen hours of light. These are the best choice for Zone 7a. They cover the middle ground and will bulb reliably during the summer months in Virginia, the Carolinas, and the Mid-Atlantic.

When you buy onion sets or seeds, check the tag or the seed packet for the daylength rating. In Zone 7a, look for intermediate-day varieties or short-day varieties planted in fall. If the tag says long-day only, it will likely struggle in this zone.

A few common intermediate or zone-7-friendly varieties include:

• Texas Yellow Giant (short-day, works in fall planting in Zone 7a)
• Yellow Texas Grano 303 (short to intermediate)
• Red Wing (short-day)
• Copra (long-day, better for late summer harvest)
• Nancy Holland (intermediate)

If you are unsure, ask at the local garden center. They know what works in your specific area.

Sets vs Seed vs Transplants

You have three ways to start onions, and each has tradeoffs.

Onion Sets

Onion sets are small, dormant bulbs about the size of a marble. You buy them in bags at the garden center and plant them directly in the ground. They are the easiest and fastest method for beginners.

The advantage of sets is speed. You skip the slow indoor seed-starting phase and get a plant growing immediately. The disadvantage is that sets are prone to bolting. Because they are already mature bulbs, they are more likely to send up a flower stalk in hot weather, which means the bulb stops growing. A bolted onion will not store well and the bulb is often small and tough.

Another issue with sets is size selection. Set bags contain a range of sizes. Discard any that are smaller than a pencil eraser. Tiny sets bolt easily. Use the larger sets for the best results.

Onion Seed

Starting onions from seed gives you the most variety to choose from and the lowest cost. A packet of seed contains hundreds of onions and usually costs less than a bag of sets.

The downside is time. Onion seeds should be started indoors eight to ten weeks before the last spring frost. They are slow to germinate and slow to grow. You need a warm, bright spot indoors and patience. If you skip the indoor phase and sow onion seeds directly in the garden, germination will be patchy and the seedlings will be small by the time the growing season warms up.

If you start from seed, sow them shallow, about a quarter inch deep, in a tray of seed starting mix. Keep the soil evenly moist. The seeds usually germinate in ten to fourteen days. When the seedlings are about the thickness of a pencil, transplant them outdoors.

Transplants

Transplants are young onion plants grown indoors from seed and sold in bundles at the garden center. They look like bunches of short green grass with tiny bulbs at the base. Transplants combine the best of sets and seed. You get the variety selection of seed and the head start of sets.

Transplants give you the most reliable result in Zone 7a. They are slightly more expensive than sets, but they bolt less often and produce larger bulbs. If you can find a good nursery that sells transplants, use them.

Which to Choose

For a beginner, onion sets are the simplest place to start. They require almost no skill. For best results and more variety, use transplants. If you want to save money and do not mind starting early indoors, use seed.

Planting

When to Plant

Onions are cold-hardy and can tolerate a light frost, but they grow slowly in cool weather. Plant them in early spring as soon as the ground can be worked. In Zone 7a, this is usually late February to mid-March. The sooner you plant, the more time the onions have to build root mass before the summer heat arrives.

If you want to overwinter onions, plant sets in the fall about four to six weeks before the first hard freeze. The plants will establish roots and go dormant, then resume growth in spring. Fall-planted onions typically produce larger bulbs than spring-planted ones because they get a head start. Not all varieties are suited for fall planting, so check the tag.

Where to Plant

Onions need full sun. They want at least six hours of direct sun per day, ideally eight to ten. They will not thrive in partial shade. Do not plant them under trees or next to tall crops that will cast shade on them.

Onions prefer loose, well-drained soil with a pH between 6.0 and 7.0. They do not like heavy clay that stays wet. If your soil is clayey, amend it with compost and consider growing onions in a raised bed.

Work two to three inches of well-aged compost into the top six inches of soil before planting. Onions are moderate to heavy feeders, so good soil at the start makes a difference.

How to Plant

Plant onion sets with the pointy end up, about one inch deep. Space them three to four inches apart in rows that are twelve to eighteen inches apart. If you want larger bulbs, space them closer to four inches. If you want smaller bulbs, space them closer to three inches.

Do not bury sets deep. Unlike potatoes or garlic, onions do not benefit from being covered with extra soil. The bulb should sit just below the surface and push upward as it enlarges.

If you are planting transplants, dig a shallow trench and set the plants in it, then fill the trench with soil up to the base of the leaves. Do not bury the leaves. Firm the soil gently around the base and water well.

If you are planting seeds directly in the garden, sow them a quarter inch deep in rows spaced twelve to eighteen inches apart. Thin seedlings to three to four inches apart once they are a few inches tall. You can harvest the thinnings as green onions.

Seasonal Care

Onions are relatively low-maintenance once they are established, but a few simple tasks during the growing season matter.

Weeding

Onions have shallow root systems and they compete poorly with weeds. This is the single most important maintenance task in an onion bed. Pull weeds by hand or use a shallow hand cultivator. Do not hill up soil on onions, as this encourages stem rot and interferes with bulb development. Keep the bed clean from planting through harvest.

Mulch helps with weed suppression and moisture retention. A one to two inch layer of straw or shredded leaves around the plants works well. Keep mulch away from the bulb itself to prevent rot.

Watering

Onions need consistent moisture, especially during the first few months of growth and when the bulbs are beginning to enlarge. Provide about one inch of water per week, more during hot and dry periods. Inconsistent watering produces uneven bulbs and can trigger bolting.

Water at the base of the plants. Wet leaves invite disease. If you water by hand, aim at the soil. A soaker hose along the row is ideal.

As the bulbs begin to mature and the lower leaves start to yellow, gradually reduce watering. Stop watering completely about two weeks before you plan to harvest. This helps the bulbs dry down and prepares them for curing.

Fertilizing

Onions are heavy feeders. They need more nutrients than lettuce and fewer than corn. If you worked compost into the soil at planting time, the onions will have enough food for the early growing phase.

Side-dress with a balanced organic fertilizer, like a 5-5-5 or a compost tea, when the onions start to bulge. This is usually about four to six weeks after planting. Do not fertilize after the bulbs begin enlarging, as excess nitrogen at that stage produces large leaves and small bulbs.

Mulching

Apply a thin layer of mulch after the plants are established and about six inches tall. This keeps the soil moist, suppresses weeds, and keeps soil temperature even. Do not mulch immediately after planting, because you want the soil to warm up as quickly as possible.

Common Problems

Bolting

Bolting is when an onion sends up a flower stalk instead of forming a bulb. It is usually caused by cold temperatures during the early growing phase, followed by warm weather. A young onion that experiences a cold snap may mistake the temperature shift as a sign that the season is over, so it flowers and sets seed.

Bolted onions will not store well. The bulb will be small and tough, and the flower stalk takes energy away from bulb development. If you notice bolts, remove the flower stalk as soon as you see it. This will not make the bulb grow larger, but it may help slightly. Use bolted onions soon. They are not candidates for long-term storage.

To prevent bolting, use fresh sets rather than old ones that have been stored too long. Cold-stored sets are more likely to bolt. Buy sets in the spring, not the previous fall. Intermediate-day varieties also bolt less often than short-day varieties planted in spring.

Onion Maggot

Onion maggots are small white larvae that tunnel into onion bulbs, causing them to rot from the inside. You will notice the first signs when a plant turns yellow and wilts suddenly, even though the soil is moist.

The best prevention is a floating row cover placed over the beds at planting time. Remove the cover when you see the first onion flowers, if the plant flowers at all. Adult onion flies lay eggs at the base of the plant, and the row cover blocks them.

Crop rotation also helps. Do not plant onions, garlic, leeks, or other alliums in the same spot two years in a row.

White Rot

White rot is a soil-borne fungal disease that affects alliums. It causes the lower leaves to yellow and the bulb to break down into white fungal masses with small black resting bodies. Once white rot is in your soil, it persists for many years.

Prevention is the only real strategy. Do not bring infected seed sets into your garden. Practice crop rotation and do not plant alliums in soil that has hosted onions, garlic, or leeks for several years. If you suspect white rot in your soil, consider growing onions in raised beds with fresh soil instead.

Leek Moth

Leek moth larvae feed on the leaves and bulbs of onions and related crops. The damage is similar to onion maggot but affects the above-ground parts of the plant. Adult leek moths are small, tan moths that lay eggs on the leaves.

A floating row cover is the most reliable control. Inspect the leaves regularly and remove any larvae you find. The moth is more common in certain regions of the eastern United States and may not be an issue in your area.

Harvesting

Knowing when to harvest is the difference between onions that store for months and onions that rot in weeks.

When to Harvest

Bulb onions are ready to harvest when about two-thirds of the tops have fallen over and turned yellow. The tops die back naturally as the bulb finishes maturing. If all the tops are still standing upright, the onions are not ready.

Some gardeners bend the remaining tops down to the soil to speed up the curing process. This is optional. The tops will fall over on their own in most cases.

If an onion sends up a flower stalk, harvest it immediately. Flowering means the bulb has stopped growing and it will not store well.

How to Harvest

Harvest onions in dry weather. Wet-harvested onions do not cure properly and are more likely to rot in storage. Use a garden fork or shovel to loosen the soil around the bulbs, then grasp the tops and pull gently. Do not drag the onions across the ground, as bruising invites rot.

Leave the onions on the soil surface for a day or two to dry in the sun, as long as the weather is dry and the forecast shows no rain. If rain is expected, move them to a covered, well-ventilated area to dry.

Curing and Storage

Curing is the process of drying the outer layers of the onion to create a protective paper-like skin. It is essential for long-term storage.

How to Cure

After pulling the onions from the garden, lay them in a single layer in a warm, dry, well-ventilated area out of direct sunlight. A covered porch, garage, or shed works well. The tops should remain attached during curing.

Let them cure for one to two weeks. The outer skin should become papery and dry. The neck (where the top meets the bulb) should be tight and dry to the touch. If the neck is still soft or damp, the onion is not fully cured and will not store well.

Preparing for Storage

Once the onions are fully cured, trim the roots to about half an inch and cut the tops to one inch above the bulb. If you prefer to braid your onions for hanging, leave the tops longer. Braid three or four onions together using the dried leaves.

Storage Conditions

Cured onions store best at forty to sixty degrees Fahrenheit with sixty-five to seventy percent relative humidity and good air circulation. A cool basement, root cellar, or ventilated closet works well.

Store onions in mesh bags, nylon stockings, or ventilated boxes. Do not store them in sealed plastic bags, as trapped moisture causes rot. Do not store onions near potatoes. Potatoes release moisture and gas that make onions spoil faster. Keep them in separate containers.

Properly cured and stored onions will keep for three to six months, depending on the variety. Storage varieties like Texas Grano and Copra keep longer than sweet varieties like Walla Walla. You can check your stored onions every month or two and remove any that show soft spots or signs of sprouting.

Using Fresh Onions

Not all onions are meant for long storage. Sweet varieties and early-season onions taste best when eaten fresh. Use them within a few weeks and reserve your best-storing varieties for winter. This way you get the best of both worlds: fresh flavor in the summer and stored bulbs through the cold months.

A Simple Onion Plan

Here is a straightforward setup for a Zone 7a beginner:

Late February to mid-March: Buy intermediate or short-day onion sets from the garden center. Pick the larger ones, discard the tiny ones.

Mid-March: Plant sets one inch deep, three to four inches apart, in full sun with compost-amended soil. Water once to settle the soil.

April through June: Keep the bed weed-free. Water about one inch per week. Side-dress with balanced fertilizer when bulbs start to swell.

Late July: Tops begin to yellow and fall over. Stop watering.

Mid-August: Pull onions in dry weather. Cure on a covered porch for one to two weeks.

September: Trim tops and roots. Store in mesh bags in a cool, dry place.

Two dozen onion plants can produce a modest supply of bulbs for a household. The yield is not as dramatic as zucchini or cucumbers, but the value per plant is higher because the onions last through the winter kitchen.

The Point of Onions

Onions are a quiet crop. They do not produce a flood of fruit like summer squash. They do not climb a trellis or demand a lot of attention. But they reward patience with storage that lasts months, flavor that defines a kitchen, and a reliable cycle that teaches you about daylength, soil, and timing.

Grow a small bed of onions once and you will understand why they are one of the oldest crops humans have cultivated. They are simple, practical, and deeply useful. Plant them in March. Keep the weeds down. Harvest when the tops fall over. Cure them well. Eat them through the winter.

That is the onion garden.

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— C. Steward 🥕