How to Grow Onions: From Seed, Sets, Transplants or an Onion You Already Have
To grow onions, choose a variety that matches your day length, plant seed, sets or transplants in full sun and loose, well-drained soil as soon as the ground can be worked, keep the soil evenly moist, and harvest when about half the tops have fallen over. Most bulb onions need about 3 to 4 months in the garden, plus 10 to 12 weeks of indoor seed-starting if you grow from seed. Short on time? Green onions are ready in roughly 25 to 80 days — see our guide to growing green onions for the fast crop.
Onions have been in gardens for more than 5,000 years. The bulb onion, Allium cepa, was already a staple in ancient Egypt — and it still earns its bed space today, because a homegrown storage onion, cured and kept right, lasts for months while you choose the exact variety your kitchen wants: sweet and fresh, or pungent and long-keeping.
Onion Growing at a Glance
| Quick Fact | What To Do |
|---|---|
| Sun | 6 to 8 hours of direct sun |
| Soil | Loose, well-drained, rich in compost; pH about 6.0 to 6.8 |
| Start | As soon as the soil can be worked — check when to plant onions by zone for your dates |
| Depth | About 1 in (2.5 cm); 1 to 1.5 in for transplants |
| Spacing | 4 to 6 in (10 to 15 cm) for full bulbs |
| Water | About 1 in (25 mm) a week |
| Time to Harvest | Seed: 10 to 12 weeks indoors, then about 3 to 4 months outside · Sets and transplants: about 3 to 4 months |
| Harvest Sign | About half the tops fallen over and dry |
| Cure | 2 to 3 weeks, warm, dry and airy |
| Store | 32 to 40°F (0 to 4°C) at 65 to 70% humidity |
Choose How You Want to Start
From Seed
Lowest cost, widest variety choice. 10 to 12 weeks indoors, then about 3 to 4 months outside. Best value if you can start trays indoors.
From Sets
The simplest start for beginners. About 3 to 4 months. Buy sets smaller than a dime.
From Transplants
Most reliable for big, dry bulbs. About 3 to 4 months. No seed-starting needed.
Full comparison table below.
Seed vs. Sets vs. Transplants: Full Comparison
| Method | Time to Harvest | Cost | Best For |
|---|---|---|---|
| Seed | 10 to 12 weeks indoors, then about 3 to 4 months outside | Lowest, widest variety choice | Big keepers, winter tray-starters |
| Sets | About 3 to 4 months | Low to medium | First-timers, cold short springs |
| Transplants | About 3 to 4 months | Higher | Big, even bulbs without starting seed |
| An onion you already have | Greens in days; bulbs unreliable | Free | Experiments and a few greens |
Starting from scratch? Our guide to growing onions from seed covers indoor sowing, germination and transplanting in full.
Which Onion Type for Your Location
Onions follow daylight, not the calendar. Pick a type that never gets its bulbing signal and you’ll harvest leaves instead of bulbs.
| Type | Daylight Needed | Where It Suits |
|---|---|---|
| Short-day | 10 to 12 hours | Southern regions, zones 7 and warmer |
| Intermediate-day | 12 to 14 hours | In-between latitudes, zones 5 to 6 |
| Long-day | 14 to 16 hours | Northern regions, zone 6 and colder |
Not sure which type matches your latitude? Our short-day vs long-day onions guide breaks down the zones and variety picks for each.
Best Onion Varieties by Day-Length Type
Match your variety to your day-length zone above — a short-day onion planted up north bulbs too early and stays small, and a long-day onion planted down south often won’t bulb at all.
Short-Day Varieties (Southern US, zones 7 and warmer)
| Variety | Color | Flavor | Storage Life |
|---|---|---|---|
| 1015Y Texas Super Sweet | Yellow | Very mild | Short (4 to 6 weeks) |
| Georgia Sweet | Yellow | Mild, sweet | Short |
| Red Candy Apple | Red | Mild | Short to moderate |
Intermediate-Day Varieties (zones 5 to 6)
| Variety | Color | Flavor | Storage Life |
|---|---|---|---|
| Candy | Yellow | Sweet | Moderate (2 to 3 months) |
| Superstar | White | Mild | Moderate |
Long-Day Varieties (Northern US, zone 6 and colder)
| Variety | Color | Flavor | Storage Life |
|---|---|---|---|
| Walla Walla | Yellow-brown | Sweet | Short (best eaten fresh) |
| Yellow Spanish | Yellow | Pungent | Long (4 to 6 months) |
| Patterson | Yellow | Pungent, firm | Very long (6 to 8 months) |
| Red Zeppelin | Red | Pungent | Long |
See every type of onion compared by flavor, best cooking use and growing ease.
How Much Should You Plant?
Onions are cheap to plant and expensive to run out of. As a planning guide:
- Fresh eating: plan on about 25 to 50 feet of row per person for dry bulb onions, or 10 to 15 feet for green onions (University of Missouri Extension).
- A 10-foot row of storage bulbs: Bonnie Plants expects roughly 8 to 10 lb at harvest. The LSU AgCenter yield table is more optimistic at about 22 lb per 10 feet, so plan on the lower figure.
- A square-foot bed: about 9 sets per square foot at close spacing — the full layout numbers are in our spacing guide.
Storage growers plant more than they think they need. A cured bulb in the pantry in February is the whole point.
The wider family is worth knowing too: bunching onions (Allium fistulosum), shallots, multiplier (“potato”) onions that multiply into clusters underground, and Egyptian walking onions that plant themselves from bulblets at the top of the stalk.
Companion Planting for Onions
Good Companions
Carrots, beets, lettuce, strawberries, tomatoes, cabbage-family crops (broccoli, kale, cabbage) and dill. Onions’ scent helps deter several common pests of these neighbors.
Plants to Avoid Nearby
Peas, beans, asparagus, and other alliums you want to keep isolated for seed-saving, such as shallots and leeks. Onions can stunt legume growth, and competing alliums invite shared pests and diseases.
How to Grow Onions, Step by Step
Planting depth and spacing for each starting method, at a glance.
- Prepare the bed. 6 to 8 hours of sun, loose soil that drains, compost worked in — see our guide to the best soil and pH for onions (aim for pH 6.0 to 6.8) for full bed prep.
- Plant at the right depth and spacing. About 1 in (2.5 cm) deep for sets and seedlings, and no deeper, or bulbing is inhibited (Dixondale). Space plants 4 to 6 in (10 to 15 cm) apart for full-size bulbs. Extension guides range from 3 to 4 in (University of Minnesota) to 6 in (Bonnie Plants), and the University of Minnesota sets transplants about 2 in deep. Wider spacing gives bigger bulbs.
- Water well after planting, then keep soil evenly moist, about 1 in (25 mm) a week.
- Feed while leaves grow. Stop nitrogen once bulbs start to swell.
- Weed shallowly. Onions compete poorly with weeds; don’t hill soil around onions you plan to store.
- Ease off at the end. Cut back food and water about a month before harvest.
Green onion tip: about two weeks before you plan to pull green onions, mound roughly 2 inches of soil around the stems. The buried stem blanches white and tender — longer white shanks, which is the part everyone wants.
When Onions Go Wrong
Why are my onions bolting (flowering instead of bulbing)?
Cold is the cause, not day length. Onions need about five leaves before they register cold, and roughly 3 to 4 weeks below 50°F can start a flower stalk before the bulb matures. Pull bolted plants and use them right away as green onions — they won’t store well. Next year, buy small, firm sets and avoid planting into a long cold snap.
Healthy leaves but no bulb forming?
Check in order: the day-length type matches your latitude, the planting date wasn’t late, the depth isn’t over 1 inch, nitrogen isn’t too high, and soil isn’t piled on the bulb’s shoulders.
Why are my onion bulbs so small?
Size depends on healthy leaf growth before bulbing starts. Match the type to your latitude, plant early, give each plant 4 to 5 inches of room, feed early then stop when bulbs swell, and let the tops fall on their own instead of breaking them over.
What do yellow leaves mean?
Usually overwatering, low nitrogen, or the start of a disease — the pattern tells you which. See the full diagnosis: Why Onion Leaves Turn Yellow.
Harvest, Cure and Store
Harvest when about half the tops have fallen over, cure for 2 to 3 weeks in a warm, dry, airy spot, then store at 32 to 40°F (0 to 4°C) at 65 to 70% humidity. Breaking tops over early gives smaller bulbs that keep less well. The full method — lifting, trimming, and fixing storage rots — is in our guide to how to harvest, cure and store onions.
Common Onion Pests and Diseases (With Treatment)
Catching these early and treating them by symptom keeps a small problem from costing you the whole bed. See our full onion pests and diseases guide for the complete treatment list.
Onion Thrips
Symptoms: Silvery streaks or white blotches on leaves; leaves turn grey and papery.
Treatment: Spray insecticidal soap or spinosad in early morning. Keep plants well-spaced for airflow and remove nearby weeds that host thrips.
Onion Maggots
Symptoms: Wilting seedlings; soft, tunneled bulbs at harvest.
Treatment: Use floating row covers at planting, rotate onion beds yearly, and avoid planting in freshly manured soil.
Botrytis Neck Rot
Symptoms: Soft, water-soaked tissue at the neck in storage; grey mold develops.
Treatment: Cure bulbs fully (neck completely dry) before storing. Avoid nitrogen late in the season and store in a cool, dry, well-ventilated space.
Purple Blotch
Symptoms: Purplish, sunken lesions on leaves, often starting at the tips.
Treatment: Apply a copper-based fungicide at first sign, improve airflow with wider spacing, and avoid overhead watering late in the day.
Downy Mildew
Symptoms: Pale yellow patches on leaves with grey-purple fuzzy growth in humid weather.
Treatment: Remove and destroy infected leaves immediately, avoid overhead irrigation, and rotate crops on a 3 to 4 year cycle.
Fusarium Basal Rot
Symptoms: Roots and basal plate turn brown and soft; the plant yellows and dies prematurely.
Treatment: No chemical cure. Remove and discard infected plants, rotate away from onions and alliums for 4+ years in that bed, and plant resistant varieties where available.
Watch: How to Harvest and Cure Onions
Curing turns a freshly pulled onion into one that keeps for months. This short video from an experienced home grower shows the harvest and curing process step by step — a good visual companion to the harvest and storage section above.
Video: “How To Harvest and Cure Onions So They Last You For Months!” by Jacques in the Garden on YouTube.
Two More Common Questions
Can You Grow an Onion From an Onion?
Yes, but set expectations: usually leafy shoots and sometimes a cluster of small bulbs, rarely a full-size storage onion.
Green Onions in Water
Keep the white base and roots in a glass, tips above water, and change the water every few days. Expect about 2 to 4 regrows.
Frequently Asked Questions
How do you grow onions for beginners?
Start with small, firm sets or a bundle of transplants matching your day-length type. Plant about 1 in deep and 4 to 6 in apart in full sun as soon as the soil can be worked, water about 1 in a week, and harvest when half the tops fall over.
How long does it take for onions to grow?
Bulb onions need about 3 to 4 months in the garden. From seed, add 10 to 12 weeks of indoor starting, for about 5 to 7 months in total. Green onions are ready in roughly 25 to 80 days. For the full timeline for every method, see how long onions take to grow.
Can you grow onions from a grocery-store onion?
Yes, if it sprouts, but expect greens or a few small bulbs rather than a full-size storage onion. Seed or sets give more reliable results — the full method is in our guide to growing onions from an onion you already have.
What fertilizer makes onions grow big?
Steady nitrogen early while leaves are growing, then stop once bulbs begin to swell. Too much nitrogen late causes thick necks and poor storage.
Can onions grow in pots?
Yes. Use a container at least 8 to 12 in deep with drainage holes, space plants 3 to 4 in apart, and water and feed more often than in a garden bed.
When should I plant onions?
Sets and transplants go in during spring, as soon as the soil is workable — around 50°F. Seed starts indoors 8 to 12 weeks before your last frost. In mild-winter zones 8 to 10, a fall planting works too.
How many onions can I grow per square foot?
About 9 sets per square foot at close spacing for modest bulbs, or 4 to 6 inches apart for full-size bulbs.
How much water do onions need?
About an inch a week, counting rain — shallow roots dry out fast, so keep moisture steady while bulbs form, then ease off as the tops fall.
Can I sow onion seed directly in the garden?
Yes, as soon as the soil is workable, but keep the seedbed moist through the two weeks germination can take. In short-season areas, transplants are the safer choice.
How many onions should I plant per person?
Plan on about 25 to 50 feet of row per person for fresh dry onions and 10 to 15 feet for green onions (University of Missouri Extension). For storage, plant more: Bonnie Plants expects roughly 8 to 10 lb from a 10-foot row, while the LSU AgCenter yield table lists about 22 lb per 10 feet.
Do onions come back every year?
Bulb onions are biennials — bulb the first year, seed the second — so they’re grown as annuals. For true perennials, grow multiplier or walking onions.
Choosing a start: Kevin Parker grows onions in his own beds in California, and in his experience sets are the simplest start, so they suit a first crop. Seed gives the widest variety choice, which matters most for storage onions. Neck rot is the usual storage loss, so cure bulbs fully in dry, moving air and check stored bulbs once a month.
Sources and How This Guide Was Checked
Figures on this page come from the university extension and grower guides below. Where sources differ, we show the range or say so. Harvest times vary with variety, start method and climate, so treat the timings in the tables as typical, not exact.
- University of Minnesota Extension: Growing onions in home gardens (planting depth, spacing, curing, seed-starting timing)
- Dixondale Farms: Onion Planting Guide (depth, spacing, leaf count)
- University of Missouri Extension, guide G6201 (feet of row per person)
- Bonnie Plants: How Much Do I Plant? (yield from a 10-foot row)
- LSU AgCenter: Expected Vegetable Garden Yields (yield per 100 feet of row)
- Ohio State University Extension: Growing Onions in the Garden (about 90 to 120 days from planting to harvest, with tops mostly fallen over)
Written by Kevin Parker · grows onions in his own beds in California. Figures are checked against university extension and grower sources, linked on each page. More about Kevin.