Onions are one of those crops that most people assume are too cheap at the grocery store to bother growing. And if you are comparing a fifty-cent bag of yellow cooking onions to the effort of growing your own, the math does not obviously favor the garden. But that comparison misses everything that makes homegrown onions worth the space. The flavor is different — sharper, sweeter, more complex. The variety selection is vast — you can grow Cipollini, Walla Walla Sweets, Red Torpedo, and Egyptian Walking Onions that no grocery store will ever stock. And the satisfaction of braiding a rope of cured onions and hanging them in the kitchen to use through winter is one of the quiet, deeply satisfying rhythms of a food garden.
Raised beds give onions exactly the conditions they need: loose, well-drained soil that bulbs can push through without restriction, consistent moisture without waterlogging, and the ability to amend the growing medium to the right fertility and pH. Onion roots are shallow and fibrous — they sit in the top six to eight inches of soil — so even a shallow raised bed provides more than enough depth. And the organized, accessible layout of a raised bed makes the close spacing that onions require (four inches apart in all directions) easy to manage and harvest.
The single most important decision in onion growing has nothing to do with soil, spacing, or watering. It is choosing the right day-length type for your latitude. Get this right and onions are straightforward. Get it wrong and you will have beautiful green tops and no bulbs. This guide starts there and covers everything through harvest, curing, and storage.
Day Length: The Critical Factor Most Gardeners Get Wrong
Onions form bulbs in response to day length — the number of hours of daylight in a twenty-four-hour period. This is not optional or gradual. It is a biological switch. When the day length reaches a specific threshold for that variety, the plant stops growing leaves and starts diverting energy into bulb formation. If the day length never reaches that threshold in your location, the plant never forms a proper bulb. This is not a matter of patience — you can leave the onion in the ground all year and it will never bulb if the day-length trigger is not met.
Short-day onions begin forming bulbs when day length reaches ten to twelve hours. They are designed for southern latitudes (roughly zone 7 and south, or below the 36th parallel) where summer days are shorter than in the north. Planted in fall or early winter in the South, short-day onions grow through the mild winter months and bulb up in spring as days lengthen past the ten-to-twelve-hour mark. Popular short-day varieties include Texas 1015Y (the classic Texas sweet onion, huge bulbs, mild flavor), Vidalia (the famous Georgia sweet onion, legally only grown in specific Georgia counties but the variety itself is available anywhere), Red Burgundy (beautiful red-purple sweet onion), and Granex (the parent variety behind Vidalia, reliable and productive).
Long-day onions need fourteen to sixteen hours of daylight to trigger bulbing. They are designed for northern latitudes (roughly zone 6 and north, or above the 38th parallel) where summer days are long. Planted in early spring as soon as the soil can be worked, long-day onions grow through spring and early summer, then bulb up as the longest days of the year arrive in June and July. Popular long-day varieties include Walla Walla (the legendary sweet onion from Washington state, enormous mild bulbs, poor storage), Yellow Sweet Spanish (large, mild, good raw), Copra (medium-sized, pungent, exceptional storage — keeps six to nine months), and Ailsa Craig (exhibition-sized sweet onion, can grow to two pounds or more under ideal conditions).
Intermediate-day (day-neutral) onions bulb when day length reaches twelve to fourteen hours, making them suitable for a broad middle band of the country — roughly zones 5 through 7, or between the 32nd and 42nd parallels. They are the most versatile type and the safest choice if you are unsure which day-length category your location falls into. Candy, Cabernet, and Sierra Blanca are popular intermediate-day varieties that perform well across a wide geographic range.
Check your latitude and choose accordingly. If you are in the South and you plant a long-day onion, it will never get the fourteen-plus hours of daylight it needs to bulb, and you will have beautiful scallions but no onion bulbs. If you are in the North and you plant a short-day onion, it will begin bulbing almost immediately in spring before the plant has grown enough leaves to support a decent-sized bulb, and you will get tiny, disappointing onions. Matching day-length type to latitude is not a suggestion — it is a requirement.
Sets, Seeds, and Transplants: Three Paths to the Same Crop
Onion sets are small, dormant onion bulbs — typically marble-sized — sold in bags at garden centers in spring. They are the easiest and fastest way to grow onions. Push them into the soil with the pointed end up so the tip is just at the surface, water, and they begin growing within days. Sets produce green onions (scallions) in as few as three to four weeks and full-sized bulbs in about ninety days.
The downside of sets is limited variety selection. Garden centers typically stock three or four varieties at most — yellow, white, red, and maybe a sweet. You are locked into whatever the supplier chose, which is rarely the best variety for your specific climate or culinary preferences. Sets are also more prone to bolting (flowering prematurely) than seeds or transplants, because the small bulb has already been through one growing cycle and may interpret replanting as a signal to complete its life cycle by flowering. If an onion sends up a flower stalk, the bulb stops developing and becomes woody at the center. Snap off the flower stalk as soon as it appears, but the bulb quality has already been compromised.
Onion seeds offer the widest variety selection by far — hundreds of varieties spanning every day-length type, color, flavor profile, and storage characteristic. Seed catalogs are where you find the interesting onions — the Cipollini for braising, the Tropeana Lunga for pizza, the Rossa di Milano for salads, the Patterson for six-month storage. Seeds are also the most economical way to grow onions in quantity. A single packet contains enough seed for a hundred or more plants.
The trade-off is time and effort. Onion seeds are slow to germinate (seven to fourteen days) and the seedlings grow at a glacial pace for the first several weeks. To grow full-sized bulbs from seed, you need to start seeds indoors ten to twelve weeks before your transplant-out date — which means late January or early February for most northern growers. The seedlings need consistent light, moisture, and occasional trimming (cutting the tops back to about four inches encourages thicker stems and stockier plants). It is a commitment, but the reward is access to varieties you cannot get any other way.
Onion transplants (also called starts or plants) are the middle ground. These are young onion seedlings — typically bundles of fifty to seventy-five bare-root plants — shipped by specialty growers in spring, timed for your planting window. They give you access to a broader variety selection than sets (though not as broad as seeds) without the ten-to-twelve-week indoor growing commitment. Transplants establish quickly, rarely bolt, and produce the largest bulbs of the three methods because they have a longer growing season than sets but arrive already past the slow seedling stage.
For most raised bed gardeners, transplants are the sweet spot. They offer good variety selection, reliable performance, low bolt risk, and big bulbs without the hassle of indoor seed starting. If you want the absolute widest variety selection and do not mind starting seeds indoors, grow from seed. If you want the absolute simplest approach and can accept limited variety choice, use sets.
Planting and Spacing
Onions are planted early — among the first crops to go into the raised bed in spring. They tolerate light frost and actually benefit from the cool growing conditions of early spring, which promote leaf growth. The more leaves a plant produces before bulbing begins, the larger the final bulb will be. Each green leaf above the ground corresponds to a ring in the bulb below. More leaves equals more rings equals a bigger onion.
Plant sets one inch deep with the pointed end up. Plant transplants at the same depth they were growing — usually about two inches deep, with roots spread downward and the green top exposed. Plant seeds a quarter inch deep if direct sowing, which is practical only in long-season climates where you can sow in late winter for a summer harvest.
Spacing is tight. Onions are one of the most space-efficient vegetable crops, and close planting is not just acceptable — it is standard practice. Space onions four inches apart in all directions in a grid pattern. A four-by-eight raised bed at four-inch spacing holds about two hundred and forty onions. That sounds like a lot, but consider that a family that cooks regularly uses six to eight onions per week — two hundred and forty onions covers roughly seven to ten months of cooking. Suddenly the math makes sense.
Use our spacing calculator to determine the exact count for your bed dimensions. For green onions harvested young as scallions, you can plant even more densely — two inches apart — and pull every other one as they size up, leaving the remaining onions at four-inch spacing to continue growing into full-sized bulbs.
Interplanting green onions among slower-growing crops is an excellent use of raised bed space. Tuck onion sets between young tomato transplants, around the edges of pepper plants, or alongside lettuce. The onions will be harvested as scallions long before the larger crops need the space.
Growing Season Care
Onions are shallow-rooted and need consistent moisture — especially during the bulbing phase when the plant is rapidly expanding the bulb. One inch of water per week is the baseline, delivered at the soil level via drip irrigation or soaker hose. Overhead watering wets the foliage and promotes fungal diseases, particularly downy mildew and purple blotch. If you must use overhead watering, do it in the morning so the leaves dry quickly in the sun.
Weeding is critical. Onion leaves are narrow and upright — they cast almost no shade on the soil surface, which means weeds get full sunlight between the plants. Onions cannot compete with weeds — they grow too slowly and their root systems are too shallow to outcompete aggressive weeds for water and nutrients. A weedy onion bed produces dramatically smaller bulbs than a clean one. Hand-weed regularly or mulch with a thin layer of straw or shredded leaves to suppress weed germination. Be gentle when weeding near onions — the shallow roots are easily damaged by aggressive hoeing or cultivating.
Fertilize with a nitrogen-rich fertilizer in early to mid-season while the plant is still in the leaf-growing phase. Fish emulsion, blood meal, or a balanced organic fertilizer applied every two to three weeks supports the vigorous leaf growth that translates directly into bulb size. Stop fertilizing when bulbing begins — you can tell because the base of the plant starts to swell visibly. Continued nitrogen feeding after bulbing starts produces soft, thick-necked bulbs that do not cure or store well.
As bulbs approach maturity, the outer layers of bulb skin begin to dry and turn papery. This is normal and desirable — those dry outer skins protect the bulb during storage. Do not hill soil up around onion bulbs the way you would potatoes. Onion bulbs should sit on the soil surface or slightly above it as they mature, with the top third of the bulb exposed to air and light.
Green Onions vs Storage Onions: Two Harvests from the Same Planting
You do not have to wait for full-sized bulbs to enjoy your onion crop. Any onion — sets, seeds, or transplants — can be harvested young as a green onion (scallion). Pull them when the stem is pencil-thick, wash off the soil, and use the entire plant — white base, green top, and all. Green onions harvested fresh from the garden have a vitality and brightness that grocery store scallions, which are often days old and limp, simply cannot match.
A smart approach is to plant at two-inch spacing with the intention of harvesting every other onion as a green onion, leaving the remaining plants at four-inch spacing to grow into full-sized bulbs. You get weeks of fresh green onions as a bonus crop while simultaneously thinning the bed to the optimal spacing for bulb production. It is efficient, productive, and eliminates the need for a separate scallion planting.
For dedicated green onion production, Evergreen Hardy White (a true bunching onion that does not form bulbs) and Tokyo Long White are the standards. These varieties produce slender, mild, tender green onions in forty to sixty days from seed and can be harvested repeatedly by cutting the greens an inch above the base — they regrow like chives. In a raised bed, a small section devoted to bunching onions provides a continuous supply of scallions from spring through fall without taking up the space that bulb onions need.
For long-term storage onions, pungent varieties with tight, dry skins store the longest. Copra (yellow, stores six to nine months), Patterson (yellow, stores eight to ten months, one of the longest-keeping varieties available), Redwing (red, stores four to six months), and Stuttgarter (yellow, grown from sets, stores four to five months) are outstanding keepers. Sweet onions like Walla Walla and Vidalia do not store well — their high sugar and water content makes them prone to rot after a few weeks. Eat sweet onions fresh and grow pungent varieties for the pantry.
Curing for Storage
Curing is the process that prepares onions for long-term storage by drying the outer skins, the neck, and the roots. A properly cured onion has dry, papery, rustling skins, a completely dry and tight neck (the narrow part where the leaves emerge from the bulb), and no moisture anywhere on the exterior. An improperly cured onion has a soft or moist neck, green or damp outer layers, and will rot within weeks in storage.
Harvest onions when the tops fall over naturally. This happens when the neck weakens as the plant finishes transferring energy from the leaves into the bulb. When roughly half the tops in the bed have fallen, gently push the remaining upright tops over by hand to speed the process — or just wait a few more days for them to fall on their own. Once the tops are down, leave the onions in the ground for five to seven more days, then pull them.
Cure onions in a single layer in a warm, dry, well-ventilated space out of direct sun. A covered porch, a garage with the doors open, or a shaded table outdoors works well. Spread them on screens, racks, or newspaper — anything that allows air to circulate around each bulb. Do not stack or pile them. Cure for two to four weeks until the necks are completely dry and the outer skins rustle when handled. In humid climates, curing takes longer and requires more airflow to prevent mold.
After curing, trim the roots to a quarter inch and cut the dried tops to about one inch above the bulb — unless you want to braid them. To braid onions, leave the dried stems long and weave them together into a rope or plait while the stems are still slightly pliable. A braided rope of onions hanging in the kitchen is functional food storage and one of the most visually satisfying sights in any home that takes cooking seriously.
Store cured onions in mesh bags, open baskets, or hanging braids in a cool (thirty-five to fifty degrees Fahrenheit), dry, well-ventilated space. A pantry, unheated room, or root cellar works well. Do not store in plastic bags, sealed containers, or anywhere with poor airflow — trapped moisture causes rot. Keep onions away from potatoes. Both crops release moisture and gases that accelerate spoilage in the other.
Properly cured and stored pungent storage onions keep for four to ten months depending on variety. Check your stored onions monthly, remove any that are softening or sprouting, and use those first. Even the best storage onions will eventually sprout as spring approaches — when they do, plant the sprouting ones in the garden and eat the ones that are still firm.
Companion Planting with Onions
Onions are one of the most versatile companion plants in the garden because their strong scent repels or confuses a wide range of insect pests. Planting onions near carrots helps deter carrot rust fly. Near brassicas (cabbage, broccoli, kale), onions help repel cabbage worms and cabbage loopers. Near lettuce and strawberries, onions discourage aphids. The allium scent masks the smell of the companion crop, making it harder for host-specific pests to locate their target plants.
Good companions for onions include carrots, beets, lettuce, Swiss chard, spinach, strawberries, tomatoes, peppers, brassicas, chamomile (said to improve onion flavor), and summer savory. Onions' narrow, upright growth habit means they cast almost no shade on neighboring plants, so they can be interplanted among shorter crops without competing for light.
Avoid planting onions near beans and peas. Alliums are widely reported to inhibit the growth of legumes, and many experienced gardeners confirm that beans and peas planted near onions or garlic grow poorly. The mechanism is not fully understood but the effect is consistent enough to respect. Keep alliums and legumes in separate beds or at opposite ends of a long bed.
Marking your onion varieties in the garden is worth the small effort, especially if you grow multiple types with different day-length requirements or storage characteristics. Our veggie marker set in cedar includes an onion marker among the twelve CNC-engraved stakes, and the deep-carved lettering stays legible through the entire growing season regardless of rain, irrigation, or sun exposure.
Frequently Asked Questions
Why did my onions flower instead of forming bulbs?
Premature flowering (bolting) in onions is triggered by cold temperatures followed by warming — the plant interprets this as having been through winter and responds by completing its life cycle with flowers and seed. Onion sets are more prone to bolting than transplants or direct-sown seeds because the set has already experienced one growing cycle and is predisposed to flower. Large sets (bigger than a dime) bolt more readily than small sets. To minimize bolting, use small sets, plant after the soil has warmed to at least forty-five degrees, and avoid planting so early that young plants experience extended periods below forty degrees. If a plant bolts, harvest and use that onion immediately — the bulb is still edible but will not store.
What happens if I plant the wrong day-length type for my latitude?
If you plant a long-day onion in the South, the plant will begin bulbing too early — as soon as the day length reaches the ten-to-twelve-hour threshold — before the plant has grown enough leaves to support a decent-sized bulb. The result is small, golf-ball-sized onions. If you plant a short-day onion in the North, the plant may never reach the bulbing trigger during its growing season, producing thick-stalked green onions but no proper bulbs. Intermediate-day varieties are the safest choice if you are uncertain about your latitude category, as they bulb at day lengths found across a broad middle band of the country.
How do I know when onions are ready to harvest?
The tops tell you. When the green foliage falls over and begins to yellow and dry at the neck, the bulb has stopped growing and is ready for harvest. Wait until roughly half to three-quarters of the tops in the bed have fallen naturally, then pull or dig the remaining onions. Leaving them in the ground for a few days after the tops fall helps the outermost skin layer begin drying, which gives you a head start on the curing process. Do not wait too long after the tops die back — onions left in warm, wet soil too long are prone to rot and resumed growth.
Can I grow onions from the root end of a grocery store onion?
Yes, though the results are limited. Cut the bottom half inch of an onion (the root end with the basal plate) and plant it cut-side up, barely covered with soil. It will sprout green tops that you can harvest as scallions within a few weeks. However, it will not grow a new full-sized bulb — the bulb has already completed its growing cycle. For full-sized bulbs, start with sets, seeds, or transplants of a variety matched to your day-length zone.
How many onions can I fit in a four-by-eight raised bed?
At the standard four-inch spacing in all directions, a four-by-eight-foot raised bed holds approximately two hundred and forty onions. At three-inch spacing (which works for smaller varieties and aggressive gardeners), you can fit over four hundred. That may sound excessive, but a household that cooks daily goes through onions fast — six to eight per week adds up to three hundred to four hundred onions per year. A single well-planted raised bed can cover a significant portion of your annual onion needs, and a braided rope of your own cured onions hanging in the kitchen is a reward that goes well beyond the grocery savings.