Onions for the Home Garden: Your First Crop From Seed to Pantry

Onions are the crop that quietly supports everything else in a home garden. You chop them for sautés, slow-roast whole heads alongside chicken, pickle a jar for sandwiches, and pull a handful of green onions for fresh garnish all from the same patch of soil.

They also do something most vegetables cannot. They store. A well-cured jar of onions sitting in the pantry will keep for months, feeding your family through the winter when very little else grows. That makes onions one of the most practical crops a home gardener can grow.

But onions have a reputation for being difficult. People buy sets from the garden center, get one mediocre harvest, and decide onions are just not worth the trouble. The problem is rarely the onion. It is usually planting timing, day length confusion, or harvesting too early.

This guide covers everything you need to grow onions successfully in Zone 7a. It covers choosing the right varieties, understanding day length, planting from seeds or transplants, seasonal care, common problems, harvesting and curing, and storing your harvest through winter.

Understanding Day Length

Day length is the single most important concept for growing onions, and it is also the most commonly misunderstood. Onions do not bulb based on temperature or age. They bulb based on daylight. A given onion variety will not form a bulb until the days reach a certain length, regardless of how big the plant looks.

This means you have to choose the right type for your location, or the plant will either never bulb, or bulb far too small to be useful.

Short-day onions begin forming bulbs when daylight reaches 10 to 12 hours. These are bred for southern regions, roughly south of the 36th parallel. They are typically planted in fall and harvested the following spring. In Zone 7a, short-day onions can work if planted early enough in the fall, but they are more reliable in milder climates.

Intermediate-day onions begin forming bulbs when daylight reaches 12 to 14 hours. This range covers the middle latitudes of the United States, including Zone 7a. If you live in Kentucky, Tennessee, Virginia, or northern Georgia, intermediate-day onions are usually your best choice.

Long-day onions need 14 to 16 hours of daylight to bulb. These are bred for northern regions, roughly north of the 36th parallel. If you plant a long-day onion in Zone 7a, it will go through the entire season producing leafy growth and may never form a proper bulb at all, because the days never get long enough at your latitude to trigger bulbing.

For Louisville and most of Zone 7a, intermediate-day varieties are the way to go. Some short-day varieties will also work if planted early in spring. You do not need long-day onions.

Choosing Your Varieties

Onions fall into three main categories by color and purpose: sweet, yellow, and red. Each type has a different flavor profile, storage life, and best use.

Sweet Onions

Sweet onions have a mild, low-sulfur flavor that makes them excellent for raw eating. They are the best choice for sliced salads, burgers, and quick pickles. The downside is that sweet onions have thinner skins and shorter storage life. They typically last two to three months in proper storage, compared to four to six months for yellow onions.

Texas Super Sweet 101 -- The most widely grown sweet onion for Zone 7a. It is an intermediate-day variety that produces large, uniform bulbs with a very mild flavor. Reliable and forgiving, this is a good first variety.

Granex 33 (Texas Early Granex) -- Another intermediate-day sweet onion that matures a little earlier. Smaller bulbs than Texas Super Sweet, but very consistent flavor.

Yellow Onions

Yellow onions have a sharper, more assertive flavor that mellows beautifully when cooked. They are the all-purpose onion for sautés, roasting, soups, and stews. Yellow onions also store the longest, making them the practical choice for gardeners who want onions through winter.

Walla Walla Sweet -- Technically a sweet onion with a rich, sugary flavor, but often grouped with yellows for its versatility. Grows large and stores well for a sweet variety. Intermediate-day.

Candy Hybrid -- A large, sweet-intermediate yellow that produces big bulbs. Good for both raw and cooked uses. Popular with home gardeners for its size and reliability.

Red Onions

Red onions have a mild to medium sharpness with a vibrant color that makes them popular for raw applications: salads, salsas, pickling, and garnishes. They store slightly less long than yellow onions but still hold up well for three to four months.

Red Burgundy -- The most popular red onion variety for home gardens. Large, deep-red bulbs with a balanced flavor that is sharp raw but sweetens when cooked. Intermediate-day.

Red Baron -- Slightly smaller than Red Burgundy but equally colorful and reliable. Good for those who want smaller bulbs for individual use.

For your first season, grow one sweet variety and one yellow or red. The sweet onion teaches you about day length behavior and early harvest. The yellow or red shows you the storage potential that makes onions special.

Seeds, Sets, or Starts?

You have three options for planting onions, and the choice matters more than most beginners realize.

Onion sets are small, immature bulbs that were grown the previous year, harvested in the fall, and stored through winter in a dormant state. They go into the ground in spring and are expected to bulb quickly.

The advantage of sets is speed. They are already partially grown, which means you get a harvest faster. They are also easy to plant. Just push them into the soil and water.

The disadvantage is that onion sets have a strong tendency to bolt. Because they are already mature enough to have formed a small bulb, the plant can be triggered to send up a flower stalk when spring warmth hits or when the days lengthen. A bolted onion does not form a proper bulb. The energy goes into the flower instead, and the result is a small, tough, unusable onion.

Sets also offer limited variety selection. The choices at your local garden center are usually generic and may not be the best type for your region.

Onion starts are young transplants grown in nursery trays. They look like a bundle of thin green grass with small white bottoms. Starts are more expensive than sets and offer slightly more variety than sets, but they share the same bolting risk because they are also partially mature.

Onion seeds are the option that most beginners skip and the one that experienced gardeners prefer. Starting onions from seed requires a little more planning. You either start them indoors six to eight weeks before the last frost or direct-sow them as soon as the soil can be worked in mid-to-late March.

The advantages are significant:

• Full variety selection. Every variety mentioned above is available as seed. You are not stuck with whatever the garden center happened to stock in a tray.
• Lower bolting rate. Young seedlings that start from true seed are much less likely to bolt than sets or starts, which are already halfway through their life cycle.
• Lower cost. A packet of onion seed costs a few dollars and contains hundreds of seeds. A tray of sets costs significantly more and produces far fewer plants.
• Transplant flexibility. If you start seeds indoors, you can move them to the garden at the perfect time. With sets, you are locked into whatever spring window happens.

The only real downside to seeds is that onions grow slowly at first. It takes time from planting to harvest. For most gardeners, that is not a problem. It is just a different pace than faster crops like lettuce or radishes.

For your first onion crop, buy seeds and start them indoors, or direct-sow as soon as the soil warms. If you want a shortcut and are okay with limited variety and some bolting risk, sets work. But seeds give you a better harvest for the effort.

Planting Onions

When to Plant

In Zone 7a, the ideal planting window depends on whether you are starting from seed or buying sets or starts.

Direct-sown seeds: Mid-to-late March, as soon as the soil can be worked. The soil should be at least 40 degrees Fahrenheit. Onions tolerate cool soil well and will establish roots before the heat of summer.

Started seeds (indoor start): Sow indoors six to eight weeks before your last frost date, which is mid-May in most of Zone 7a. That puts your sow date in late February to early March. Transplant them outside four to six weeks after the last frost, so early to mid-May.

Sets or starts: Mid-to-late March for early plantings, or any time through April. Plant them as soon as the ground is workable. If the soil is frozen or waterlogged, wait. Wet soil around onion bulbs invites rot.

Fall planting (optional): In Zone 7a, you can plant short-day or intermediate-day onion sets in late October to overwinter. The plants establish roots in the fall, go semi-dormant through winter, and resume growing in early spring. They typically produce a slightly earlier harvest than spring-planted onions. Fall planting works best with sets rather than seeds, because seeds need more time to establish before winter.

How to Plant

The planting method depends on whether you are direct-sowing seeds or transplanting.

Direct-sowing seeds: Scatter seeds 1/4 to 1/2 inch deep in rows spaced 12 to 18 inches apart. Thin the seedlings to 3 to 4 inches apart once they are a few inches tall. If you want larger bulbs, leave 6 inches between plants. For more, smaller scallion-type onions, leave 2 to 3 inches apart.

Transplanting (seeds started indoors, sets, or starts): Dig a narrow trench about 2 inches deep. Place onion bottoms in the trench, spacing them 4 to 6 inches apart. Cover with soil so the top of the bulb is just at the surface. Do not bury the bulb deeper than the soil line was on it when you received it. Onion bulbs do not produce adventitious roots along the stem the way tomatoes do, so planting deeper does not help and can cause rot.

For a wider-row method that works well for home gardens, sow seeds or set transplants in a wide bed that is 2 to 3 feet wide, spacing plants 6 inches apart in a staggered pattern. This works well because onions do not compete aggressively for light and the narrow rows between plants stay manageable for weeding.

Soil and Sun

Onions need full sun. At least six hours of direct sunlight daily, ideally eight or more. They also need well-drained soil. They do not tolerate waterlogged conditions at all.

The ideal soil pH for onions is between 6.0 and 6.8. Work two to three inches of compost into the planting bed before planting. Onions are moderate feeders. They benefit from balanced nutrition but do not need heavy fertilizer. Too much nitrogen encourages excessive leaf growth at the expense of bulb development.

Growing Through the Season

Once your onions are in the ground, the growing season breaks into three phases:

Establishment phase (first two to three weeks): The plant focuses on developing roots and pushing up its first true leaves. Keep the soil evenly moist. Water regularly if you do not get rainfall.

Vegetative growth phase (four to eight weeks): The plant is building foliage. This is the longest phase. During this time, keep the area weed-free. Weeds compete with young onions for nutrients and moisture. Onions are shallow-rooted and do not compete well against established weeds.

Bulbing phase: Triggered by day length, this is when the plant stops producing new leaves and starts swelling the bulb at the base. This phase can last four to eight weeks depending on variety and temperature. During bulbing, consistent water is critical. Inconsistent watering during bulbing leads to small, split, or cracked bulbs.

Watering

Onions need about one inch of water per week during the growing season. During hot, dry weeks in Zone 7a summer, increase to one and a half inches. The soil should be evenly moist, never soggy and never bone dry.

Water at the base of the plants, not overhead. Wet foliage invites fungal disease. Drip irrigation or soaker hoses work well. If you water by hand or with a hose, water early in the morning so any moisture on the leaves dries quickly.

Stop watering when the tops begin to fall over naturally. This signals that the bulbs have finished swelling and are entering the curing phase. Continuing to water at this stage delays maturation and invites rot.

Weeding

Weed onions frequently, especially during the vegetative growth phase. Hand-pulling works best for small patches. A narrow hoe works between wider rows. Avoid digging near onion plants, as the shallow roots are easily damaged.

Onions produce natural allelopathic chemicals that suppress some weed germination, but they do not eliminate the need to weed entirely. Stay on top of it.

Fertilizing

Onions benefit from a moderate application of balanced fertilizer at planting time. A compost side-dress or a light application of a balanced organic fertilizer (such as 5-5-5) works well. Side-dress again when bulbing begins.

Do not over-fertilize. Excess nitrogen during bulbing encourages soft growth that stores poorly and is more susceptible to disease.

Common Problems

Onion Fly

Onion fly lays eggs at the base of onion plants. The larvae bore into the bulb and feed, causing the plant to wilt and die from the inside out. This is more of a problem in cool, wet springs.

Prevention includes covering newly planted onions with a floating row cover for the first few weeks to prevent egg-laying. Remove the cover once the plants are established. Crop rotation also helps, as onion fly overwinters in the soil near its host plants.

Thrips

Thrips are tiny, slender insects that feed on onion leaves by scraping the surface and sucking out the plant juices. Infested leaves show silvery streaks and become dry and brittle at the tips.

In small numbers, thrips are manageable with a strong spray of water dislodging them. Insecticidal soap works for heavier infestations. Encouraging beneficial insects like predatory mites and lacewings provides natural control over time.

Downy Mildew and White Rot

Downy mildew appears as a fuzzy purple-gray growth on the leaves, usually in cool, wet weather. White rot is a soil-borne fungal disease that causes bulbs to rot from the inside, often with a white mycelial growth and small black resting structures in the soil.

Both are prevented by good drainage, avoiding overhead watering, and rotating onion plantings to a different part of the garden each year. Do not plant onions, garlic, or leeks in the same spot more than once every three to four years.

If downy mildew appears, remove the worst-affected leaves and improve air circulation. White rot is more serious because the fungus persists in the soil. If you suspect white rot, remove and destroy the affected plants and do not plant alliums in that spot for several years.

Bolting

Bolting is when an onion sends up a flower stalk before the bulb has finished forming. Once bolted, the onion will not produce a proper bulb. The energy that should go into the bulb goes into the flower instead.

Bolting is most commonly caused by onion sets (which are already partially mature), temperature swings, or plants that were started too early and got too large before being transplanted.

If you see a bolt, remove the flower stalk immediately. In some cases, the plant will redirect energy back into the bulb, though this rarely recovers a full-size onion. Use bolted onions for green onion purposes or cook them rather than storing them.

Harvesting and Curing

When to Harvest

Onions are ready to harvest when the tops begin to fall over naturally. This is not something you force. The plant signals readiness by dropping its leaves. When about half of your plants have toppled over, it is time to start pulling.

Gently lift the bulbs from the soil with a digging fork or by hand. Brush off loose soil. Do not wash them. Do not pull by the tops, as this can damage the bulb neck and invite rot.

Leave the tops attached. They will help dry the bulb during curing.

Curing

Curing is the process of drying the onion neck and outer layers so the onion can be stored long-term. Skipping curing is one of the most common beginner mistakes. Without proper curing, onions will not store well and are likely to rot within weeks.

To cure onions:

• Place harvested bulbs in a warm, dry, well-ventilated spot. A covered porch, garage, or shed with good air circulation works well.
• Spread them in a single layer on a screen, rack, or clean surface. Do not pile them in a basket during curing, as trapped moisture invites mold.
• Leave them there for two to three weeks. Turn them once or twice during curing so all sides get air.
• The onions are cured when the necks are completely dry and tight, the outer skins are papery and crinkly, and the roots are dry and shriveled.

If you expect rain during the curing period, bring the onions inside or cover them with a tarp. Onions that get wet during curing will not cure properly.

Cutting and Cleaning

Once the onions are fully cured, trim the roots to about a half inch and cut the tops to about one to two inches above the bulb. Some gardeners braid soft onion tops together and hang the bunches for storage. This works well for intermediate-storage onions but is less practical for long-term storage.

Brush off any loose outer skins. Do not remove tight-fitting outer layers, as they protect the bulb during storage.

Storing Your Onions

Properly cured onions stored under the right conditions will keep for months:

Yellow onions: Four to six months. The longest storage life. Store in a cool, dry, well-ventilated area.

Red onions: Three to four months. Good storage, though they dry out faster than yellows.

Sweet onions: Two to three months. Shorter storage life due to thinner skins and higher moisture content. Consider using sweet onions first.

For best results:

• Store in a cool, dry place between 32 and 40 degrees Fahrenheit. A basement, root cellar, or unheated spare room works well.
• Do not store onions in plastic bags. They need air circulation. Use mesh bags, baskets, or wooden crates with gaps.
• Keep them away from potatoes. Potatoes release moisture and gases that cause onions to spoil faster. Store them in separate containers.
• Check your stored onions every few weeks and remove any that show signs of softening or sprouting.

Green onions (scallions) do not store long-term. They keep in the refrigerator for one to two weeks in a damp paper towel inside a breathable bag.

Your First Onion Patch

For your first season, start small. A bed that is four feet wide and ten feet long will give you 40 to 60 onion plants. That is enough to produce a meaningful harvest without overwhelming your attention.

Here is a practical plan:

• In late February or early March, start onion seeds indoors in small containers with seed starting mix.
• In mid-to-late March, plant some sets or starts directly in the garden as a backup.
• Transplant your indoor seeds outside in mid-to-early May, spacing them 6 inches apart.
• Keep the bed weed-free and water consistently through summer.
• Harvest when the tops fall over naturally, usually July through August in Zone 7a.
• Cure for two to three weeks, then store in a cool, dry, ventilated space.

By the time you have harvested, cured, and stored your first batch of onions, you will understand why this crop is worth the patience it takes. There is a particular satisfaction in pulling onions from the pantry in January, brushing off the papery skin, and cutting into something you grew from a tiny seed in March. That kind of connection to your food does not come from buying produce at the store.

---

— C. Steward 🥕