If I had to choose one thing to grow in the garden that makes everything else in the kitchen better, it would be onions — and it would not even be a close call.
Onions have been in my garden every single year for as long as I have had a garden. They were in my mother’s garden before that, and in her mother’s garden before that. An onion is the backbone of Southern cooking. It goes into the pot before almost anything else, and without it, half the recipes I know would fall flat. Growing your own means you always have them when you need them, and the flavor of a homegrown onion — pulled right from the dirt, with the papery skin still damp — is something the grocery store cannot touch. By the time you finish this guide, you will know how to grow onions from start to finish, how to cure them so they last through winter, and how to pick the right varieties for where you live.
Getting to Know the Onion
Onions grow as a bulb underground with hollow, tubular green leaves rising straight up from the top. Depending on the variety, the bulb can be anywhere from the size of a golf ball to bigger than your fist. The skin ranges from deep golden brown to white to dark red-purple, and the flesh inside can be white, yellow, or tinged with red. The leaves are waxy blue-green and can reach eighteen inches to two feet tall when the plant is growing strong.
What makes onions interesting is how they form their bulbs. It is not about how long they have been in the ground — it is about day length. When the days get long enough, the plant stops making leaves and starts putting all its energy into swelling that bulb. This is the single most important thing you need to understand about growing onions, and I will get into it more in a moment.
The common onion (Allium cepa) has been cultivated for thousands of years, going back to central Asia. It traveled the world with every civilization that grew it because everyone figured out the same thing — food tastes better with onions in it. In the South, onions have been a kitchen garden staple since the first settlers put seeds in the ground. You will hear them called cooking onions, bulb onions, storage onions, or sweet onions depending on the variety and where you are. The famous Vidalia onion out of Georgia is just a particular sweet variety grown in particular soil, but it put Southern onions on the map in a way nothing else has.
The Day Length Secret — Why This Matters More Than Anything
This is where most people go wrong with onions, and I want to make sure you understand it before you buy a single seed or set. Onions are classified by how much daylight they need to start forming a bulb. Get this wrong, and you will grow beautiful green tops with a bulb no bigger than a marble.
Short-day onions start forming bulbs when they get about 10 to 12 hours of daylight. These are the onions for the South — anywhere roughly from zone 7 southward. They get planted in the fall or very early spring and bulk up as the days lengthen through spring. If you are in the Deep South, Gulf Coast, or anywhere the winters are mild, short-day onions are what you want.
Long-day onions need 14 to 16 hours of daylight to trigger bulbing. These are for Northern gardeners. If you plant a long-day onion in the South, our days never get long enough to trigger a decent bulb, and you end up disappointed. Leave these to the folks up North.
Intermediate-day onions, sometimes called day-neutral, fall in the middle and need about 12 to 14 hours. These work in the middle of the country — roughly zones 5 through 7 — and can sometimes do well in the Upper South.
For us in the South, the best short-day varieties include Texas 1015Y (the supersweet yellow), Vidalia types like Yellow Granex, Red Burgundy, and White Bermuda. These are proven performers in Southern heat with mild, sweet flavor. If you are in the Upper South or the transition zone, try intermediate-day varieties like Candy, Sierra Blanca, or Red Candy Apple.
What the Ground Needs
Onions are hungrier than most people expect. They are not like beans that feed themselves — onions want rich, loose, well-drained soil and regular feeding throughout their growing season. The better you prepare the ground, the bigger and healthier your bulbs will be.
The soil should be loose and crumbly, the kind where you can push your fingers into it without much effort. Onions are trying to swell underground, and if the soil is tight and compacted, the bulb has to fight for every fraction of an inch. Sandy loam is ideal. If you have clay, and I know many of you do, work in plenty of compost and coarse sand until the soil feels open and light in your hand. Raised beds are an excellent choice for onions if your native soil is heavy.
Aim for a pH between 6.0 and 6.8. Onions prefer things just slightly on the acidic side of neutral. A simple soil test will tell you where you stand, and a little lime or sulfur will adjust it if needed.
Before planting, work in two to three inches of good finished compost and a balanced organic fertilizer. Onions need consistent nitrogen to keep pushing out leaves — each leaf corresponds to a ring in the bulb, so more healthy leaves means a bigger onion. Side-dress with a nitrogen-rich fertilizer like blood meal or fish emulsion every two to three weeks during the growing season. Stop feeding once the bulbs start to swell and the necks begin to soften — at that point the plant needs to focus on finishing the bulb, not making new leaves.
Mulch lightly with straw or finely shredded leaves. Keep the mulch thin — an inch or so — because onions like the soil surface to be warm, and too much mulch keeps things too cool and damp around the neck, which invites rot.
Sun and Water for Good Bulbs
Onions want full sun — at least six to eight hours a day, and more is better. Since day length is what triggers bulbing, you want your onion patch in the sunniest spot you have. Shade means fewer hours of light reaching the plant, and that can delay or reduce bulb formation.
If the green tops start flopping over or looking pale and thin instead of standing upright and blue-green, the plant may not be getting enough light. It can also mean a nitrogen deficiency, so check both.
Watering onions is about consistency. They have shallow roots and cannot reach deep for moisture, so they need regular, even watering — about an inch per week, split into two or three waterings rather than one big soak. Drip irrigation or a soaker hose is best. The goal is to keep the top few inches of soil evenly moist but never soggy.
Overwatered onions develop soft, mushy outer layers and are magnets for rot. The roots sit in the top four to six inches of soil, and if that zone stays waterlogged, the bulb will spoil from the bottom up. You might not notice until you pull it and find a slimy mess.
Underwatered onions stop growing. The leaves start to yellow from the tips down, and the plant may bolt — sending up a flower stalk in a panic to reproduce before it dies. Once an onion bolts, the bulb is ruined for storage because the hard flower stalk runs right through the center. You can still eat a bolted onion, but use it right away.
Water in the morning so the foliage dries quickly. Stop watering entirely when the tops begin to fall over and the necks soften — that is the plant telling you it is done growing. Adding water at that point delays curing and promotes rot.
Three Ways to Start Your Onions
You can start onions from seeds, sets, or transplants, and each method has its place. I have used all three, and the right choice depends on your patience and your growing season.
From Seed
Starting from seed gives you the widest variety selection and the best bulbs, but it takes time and planning. For Southern gardens, start seeds indoors eight to ten weeks before your transplant date. In the Deep South, that means starting seeds in late November or December for a late January or February transplant. Farther north, start in January or February for a spring transplant after your last frost.
Sow seeds in flats or cell trays, about a quarter inch deep, in a good seed-starting mix. Keep them moist and warm — around 65 to 75 degrees. They will germinate in seven to fourteen days. The seedlings look like tiny blades of grass at first, and they are slow growers. Do not let them dry out.
When the seedlings are about the thickness of a pencil and six inches tall, they are ready to transplant. Some people give them a “haircut,” trimming the tops back to about four inches, which encourages stockier growth and makes them easier to handle during transplanting.
From Sets
Onion sets are small, dormant bulbs about the size of a marble. You can find them at every garden center in the spring. They are the easiest way to grow onions — just push them into the soil and they take off. But they have a downside. Sets are more likely to bolt than transplants because they have already been through one growth cycle. They also tend to produce smaller bulbs.
If you use sets, choose the smallest ones in the bag. Bigger sets look tempting, but they are more likely to bolt. Plant them pointy end up, just barely covered with soil so the tip is at or just below the surface.
From Transplants
Transplants — sometimes called onion slips or starts — are young seedlings that someone else started for you. They come in bundles of fifty or a hundred, often sold bare-root with the roots dangling. This is my favorite way to grow onions. You get the variety selection almost as good as seed, without the months of babysitting seedlings under grow lights.
When you get transplants, separate them gently and plant them about an inch deep, four to six inches apart. If they look wilted and sad when they arrive in the mail or come home from the nursery, do not worry. Trim the roots to about an inch, trim the tops to about four inches, soak the roots in water for an hour, and plant them. They will perk up within a few days.
Getting Them in the Ground
Timing is everything with onions. In the Deep South, short-day onions go in the ground in late fall — October through December — so they can establish roots through the mild winter and bulb up in spring. In the Upper South, plant in late winter or very early spring, as soon as the ground can be worked. Onions can handle a light frost without flinching, so do not wait for warm weather. They actually prefer cool conditions for the leaf-growing phase.
Prepare your bed first. Loosen the soil at least eight inches deep, work in your compost and fertilizer, and rake it smooth. Make shallow furrows about an inch deep and four to six inches apart within the row. Space the rows twelve to eighteen inches apart.
Set each transplant or set into the furrow, firm the soil around it, and water gently. If you are planting from transplants, make sure the roots are pointing down and the tiny bulb base is covered but not buried deeply — an inch of soil over the roots is plenty. For sets, pointy end up, just barely covered.
After planting, water everything in well. A light application of mulch between the rows keeps weeds down, but keep it away from the base of the plants. Onions need air circulation around the neck.
Container growing works for onions, especially green onions and smaller bulbing varieties. Use a wide, shallow container — at least eight inches deep and as wide as you can manage. A half whiskey barrel works beautifully. Fill with a good potting mix enriched with compost, and space plants three to four inches apart. You will get smaller bulbs than in-ground, but they will be fresh and delicious.
What to Plant Nearby — and What to Keep Away
Onions are one of the best companion plants in the garden because their strong scent deters many pests. Plant them alongside carrots — the onion smell confuses the carrot fly, and the carrot scent confuses the onion fly. It is one of the oldest companion planting partnerships in the book, and it works.
Onions also do well planted near beets, lettuce, tomatoes, peppers, strawberries, and members of the cabbage family. Their scent helps keep aphids, Japanese beetles, and rabbits at bay. A border of onions around your garden beds is a natural pest deterrent.
Keep onions far away from beans and peas. Alliums and legumes do not get along — the onions seem to stunt the growth of beans, and the relationship does not benefit either side. Also keep them away from asparagus and sage, which compete poorly with the allium family.
Pests and Problems in the Onion Patch
Onions are relatively tough, but they have their share of enemies, especially in warm, humid climates.
Pests
Onion thrips are the most common pest, and they are tiny enough that you might not see them at first. Look for silvery streaks or patches on the leaves — that is thrip feeding damage. If you look closely, you will see the insects themselves, barely visible, hiding in the leaf folds. A strong blast of water dislodges them. For heavy infestations, a spray of neem oil or insecticidal soap applied to the leaf crevices where they hide will knock them back. Blue sticky traps near the onion bed catch adults.
Onion maggots are the larvae of a small gray fly that lays eggs at the base of the plant. The maggots burrow into the bulb and destroy it from the inside. The first sign is usually a plant that suddenly wilts and dies despite adequate water. Pull it up and you will find tunnels through the bulb. Row covers installed at planting time keep the flies from laying eggs. Rotating your onion patch helps break the cycle.
Cutworms can clip young transplants right at the soil line, the same way they attack other seedlings. Cardboard collars around each plant at transplanting time stop them.
Diseases
Downy mildew shows up as pale green or yellowish patches on the leaves, often with a grayish fuzz on the underside. It is worst in cool, damp weather — exactly the conditions of a Southern winter garden. Good air circulation and wide spacing help prevent it. Remove and destroy affected leaves promptly.
Botrytis leaf blight, sometimes called gray mold, causes oval-shaped white spots with green halos on the leaves. It spreads rapidly in wet conditions. Again, air circulation is your friend. Avoid overhead watering and space your plants so air can move freely between them.
Purple blotch starts as small, water-soaked lesions that turn dark purple with yellow edges. It thrives in warm, humid weather and spreads by rain splash. Keep the foliage as dry as possible and remove infected leaves immediately.
Fusarium basal rot attacks the base of the bulb, causing it to soften and collapse. The roots discolor and die. There is no cure once it takes hold — pull and destroy affected plants. Avoid planting onions in the same spot for at least four years after a fusarium problem.
Knowing When Your Onions Are Ready
Harvesting onions is one of the most satisfying moments in the garden, and the timing is not hard to read once you know what to look for.
As the bulbs reach full size, the tops begin to weaken at the neck and fall over. When about half to two-thirds of the tops in your patch have flopped, it is time. Do not push the remaining tops over — let them fall naturally. Forcing them can damage the neck and open the door to rot during storage.
Choose a dry day. Loosen the soil around each bulb with a garden fork — do not just yank them out or you risk bruising the bulb. Lift them gently and lay them on top of the soil or on a screen in the sun. Let them sit there for a day or two if the weather is dry. The outer skins will start to dry and tighten.
Pick up a cured onion and look at the neck where the leaves meet the bulb. If the neck is still thick and green, it needs more time. When the neck feels thin, dry, and papery — like it has shriveled tight around the stem — the onion is ready for long-term curing.
Curing and Storing Your Harvest
Curing is what turns a fresh onion into a storage onion, and it is not optional if you want them to last. After the initial field drying, bring your onions to a warm, dry, well-ventilated space — a covered porch, a garage, a barn, anywhere with good airflow and no direct rain.
Spread them out in a single layer on screens, wire racks, or hang them in mesh bags or old pantyhose. They need air circulating all around them. Let them cure for two to four weeks. You will know they are ready when the outer skins are dry and papery, the necks are completely tight and dry, and the roots are wiry and dry.
Trim the tops to about an inch above the bulb and trim the roots close. Or, if you prefer the old way, braid the dried tops together and hang the braid in your pantry — it looks beautiful and keeps the onions accessible.
Store cured onions in a cool, dry, dark place with good air circulation. A mesh bag, a wire basket, or a pantyhose leg with knots between each onion all work well. Ideal storage temperature is 35 to 50 degrees. A cool basement, root cellar, or unheated closet is perfect. Do not store them near potatoes — the moisture and gases each one gives off will spoil the other.
Sweet onions like Vidalias do not store as long as pungent storage varieties. Plan to use sweet onions within a month or two. Pungent yellow storage types can last three to six months or longer if properly cured. Any onion with a thick neck, a soft spot, or a green sprout should be used immediately, not stored.
Freezing
If you have more onions than you can store or use before they go soft, chop them and freeze them. Dice the onions, spread them on a sheet pan in a single layer, and freeze until solid. Then bag them in freezer bags with as much air pressed out as possible. They will be soft when thawed — no good for fresh eating — but perfect for cooking, and they keep for six months or more in the freezer.
Saving Seed
Onion seed saving takes two years because onions are biennial — they form a bulb the first year and flower the second. To save seed, select your best bulbs at harvest, cure them, store them through winter, and replant them in spring. They will send up a tall flower stalk topped with a round cluster of tiny white or purple flowers. When the seed heads dry and the black seeds are visible, cut the heads, dry them further indoors, and shake the seeds out. Onion seed loses viability fast — use it within one to two years for best germination.
Year-Round Care for the Onion Patch
In the South, the onion calendar runs different from most of the country because our short-day varieties go in the ground during fall.
Fall is planting season. Get your transplants or sets in the ground from October through December in the Deep South. This gives them the cool, short days they need to establish roots and grow leaves. Feed lightly at planting and again every two to three weeks through winter.
Winter is the leaf-building phase. The plants look like they are barely doing anything, but below the surface the roots are spreading and the plant is banking energy. Keep them watered during dry spells — winter drought is real in the South, even if it does not feel like it. Watch for thrips and downy mildew in damp weather.
Spring is when everything happens. As the days lengthen past that 10 to 12 hour mark, bulbing kicks in. Keep up with feeding until you see the bulbs starting to swell, then stop. Water consistently. This is the critical period — stress now means small bulbs.
Late spring to early summer is harvest time. When the tops fall over, pull them, cure them, and get them stored. After harvest, clean out the bed and plant something else — beans are a perfect follow-up crop because they will fix nitrogen that the heavy-feeding onions pulled out.
The Mistakes I See People Make Every Year
Growing the wrong day-length variety is the number one mistake, and I cannot say it enough. If you are in the South and you plant a long-day onion, you will get green tops and no bulb worth mentioning. Check the variety before you buy. Ask if you are not sure. This one mistake accounts for more onion failures than everything else on this list combined.
Planting too deep is another common one. Onions want to be barely buried — an inch of soil over the base is plenty. If you bury them like you would a tomato transplant, the bulb has to fight its way to the surface, and it often ends up misshapen or undersized.
Not feeding enough is the mistake of people who treat onions like a low-maintenance crop. Onions are heavy feeders. Every leaf the plant produces becomes a ring in the bulb. If you starve the plant, you get a small bulb with few layers. Feed regularly through the growing season.
Letting weeds take over the onion bed is devastating because onions have shallow roots and thin leaves — they cannot compete. Weeds steal moisture and nutrients right from the zone where onion roots are feeding. Keep the bed clean, especially when the plants are young. Hand weed carefully to avoid disturbing those shallow roots.
Watering right up until harvest seems logical, but it ruins storage quality. Once those tops start falling, the onion is telling you it is done. Stop watering and let it cure in the ground for a few days before pulling.
Skipping the curing step is the mistake that wastes an entire harvest. People pull onions and put them straight in a bag or the pantry, and within a few weeks they are soft and moldy. Proper curing takes two to four weeks, and it is the difference between an onion that lasts a week and one that lasts six months.
Storing onions with potatoes is a mistake that ruins both crops. They give off gases and moisture that accelerate each other’s decline. Keep them in separate areas, preferably in separate rooms.
Growing Onions in the Southern Garden
The South is one of the best places in the country to grow onions, and the reason is simple — our mild winters let us plant in fall and grow through the cool season, which is exactly what short-day onions prefer. While Northern gardeners are shoveling snow, our onions are quietly putting down roots and building the leaf growth that becomes next spring’s bulbs.
Heat is not the enemy people think it is for Southern onions. The trick is that the bulbing and harvest happen before the worst of summer arrives. By the time July hits, your onions should be cured and in storage. If they are still in the ground in full summer heat, something went wrong with timing.
Our biggest challenge is moisture and humidity during the winter and spring growing season. Fungal diseases love the damp, mild conditions we get from November through April. Wide spacing, good drainage, and morning watering are your best tools. Raised beds that drain fast and warm up quickly in spring are worth their weight in gold for onion growing in the South.
Red clay soil is a real obstacle for onions. That tight, dense clay fights against bulb expansion and holds water too long around the roots. If you have clay, either build raised beds filled with good soil or work the native ground heavily with compost and coarse sand over several seasons. I have seen people try to grow onions in unimproved Georgia clay, and it just does not work.
Vidalia onions are the pride of Georgia, and they deserve the reputation. But what most people do not realize is that the famous sweetness comes as much from the soil as from the variety. The low-sulfur soil around Vidalia, Georgia produces that mild, sweet flavor. You can grow the same Yellow Granex variety in different soil and get a noticeably different taste. Still a good onion, but not the same. If you want the closest thing to a Vidalia from your own garden, test your soil sulfur levels and choose accordingly.
For Southern container gardeners, onions do well in wide, shallow pots on a sunny porch or patio. Green onions are especially easy in containers — plant thickly and start pulling them when they are pencil-thick. For bulbing onions, give each plant at least three to four inches of space and use a quality potting mix with added compost.
Now Go Fill That Onion Bed
Growing onions takes a little more planning than some crops, but the reward is sitting in your kitchen in the middle of January with a braid of homegrown onions hanging on the wall and knowing you grew every single one. There is nothing in the store that compares to the flavor of an onion you pulled from your own dirt, cured in your own sunshine, and stored with your own hands.
The key is simple — pick the right variety for your latitude, give them good loose soil, feed them well, water them steady, and be patient. When those tops fall over and you pull that first perfect golden bulb out of the ground, you will understand why onions have been at the center of the kitchen garden for as long as anyone can remember.
Get your transplants ordered. Get your bed ready. The onions are waiting on you.
