Onion Seeds – Allium cepa
Allium cepa • Amaryllidaceae • Native to Central Asia, Middle East
Onion Seeds grow into versatile bulb-forming plants valued for their crisp texture, layered bulbs, and savory flavor. A practical choice for kitchen gardens, raised beds, containers, and everyday home cooking.
Plant Name: Onion Seeds
Quantity: 100
Selected: Onion Seeds / 100
Germination depends on soil, temperature, moisture, and care. See our return policy for details.
At a glance
Onions, including their seeds, foliage, and bulbs, are toxic to dogs, cats, and many other pets, so plant them in areas your animals cannot access and handle any clippings carefully.
Botanical profile
Meet the Onion – Allium cepa
Step-by-step planting
Growing onions from seed takes patience and attention to timing, but following a consistent onion growing guide from sowing through harvest gives you the kind of control over your crop that sets experienced gardeners apart.
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1
Choose the Right Variety for Your Latitude
Before you sow a single seed, confirm whether your region needs long day onion varieties, which require 14 or more hours of daylight to bulb up and suit northern gardens, or short day onion varieties, which bulb with around 10 to 12 hours of light and thrive in southern climates, because planting the wrong type is the most common reason onions fail to form proper bulbs.
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2
Start Seeds at the Right Soil Temperature
Onion seed germination works most reliably when the growing medium stays between 65 and 75 degrees Fahrenheit, so if you are starting seeds indoors in late winter, a seedling heat mat can help maintain that range consistently.
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3
Sow Indoors 10 to 12 Weeks Before Transplant Date
When learning how to plant onion seeds indoors, sow them about a quarter inch deep in shallow trays or cells filled with a fine, well-draining seed-starting mix, then keep the surface evenly moist but not waterlogged.
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4
Provide Plenty of Light
Onion seedlings become leggy and weak without strong light, so position them under grow lights for 14 to 16 hours a day or in the sunniest south-facing window you have, trimming the tops back to about 3 inches if they flop over.
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5
Harden Off Before Transplanting
About a week before moving seedlings outside, set them outdoors in a sheltered spot for a few hours each day, gradually increasing their exposure to direct sun and wind so they are not shocked by the transition.
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6
Follow Correct Onion Seed Spacing at Planting
When transplanting into the garden, follow standard onion seed spacing guidelines and set seedlings 4 to 6 inches apart in rows 12 inches apart, planting them just deep enough that the roots are covered and the base of each seedling sits at or slightly above soil level.
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7
Monitor for Harvest Readiness
Onion harvest time comes when roughly half to two thirds of the tops have naturally fallen over and begun to yellow, at which point you should stop watering, let the bulbs support in place for a few days if the weather is dry, then lift them gently and allow them to dry in a warm, airy spot for two to four weeks before storage.
Year-round care
Spring
- Sow after last frost
- prepare soil with compost
Summer
- Water regularly
- feed monthly
Fall
- Harvest before frost
- store well
Winter
- Rest
- store seeds cool and dry
Full specifications
Shipping
- Orders are delivered within 8 to 16 business days.
- All orders include tracking.
- Free shipping on all orders.
- Seeds are packed in moisture-resistant, resealable foil packets.
Germination
Germination rates vary depending on climate, soil conditions, and care. Seeds perform best when planted in the right season at the correct temperature, with consistent moisture and adequate light. We take quality seriously and each batch is tested before packaging. If you have concerns about your seeds, reach out and we will do our best to help.
Frequently asked
Questions about Onion Seeds – Allium cepa
How long do onion seeds take to germinate?
Under good conditions, with steady moisture and soil temperatures in the 65 to 75 degree Fahrenheit range, onion seeds commonly sprout within 7 to 14 days. That said, onion seed germination can stretch to three weeks or more if temperatures are cool, the soil dries out between waterings, or seeds are older. Keeping conditions consistent is more important than any single factor.
What is the best soil temperature for onion seed germination?
Onion seeds germinate most reliably in a soil or growing medium held between 65 and 75 degrees Fahrenheit. Below 50 degrees germination slows dramatically and becomes erratic, while temperatures above 85 degrees can also reduce the rate of sprouting. A seedling heat mat with a thermostat takes the guesswork out of maintaining that window indoors.
Should I start onion seeds indoors or direct sow?
In most climates, starting onion seeds indoors 10 to 12 weeks before your last frost date gives seedlings a long enough head start to develop full-sized bulbs before summer. Direct sowing works well in mild-winter climates where gardeners can sow in fall for a late spring harvest, particularly with short day onion varieties. If your growing season is short, indoor starting is almost always the more reliable approach.
How deep should onion seeds be planted?
Plant onion seeds about a quarter inch deep, which is shallow enough that the seed can push through without exhausting itself but covered enough to stay in contact with moist growing medium. Pressing the surface gently after sowing helps ensure that contact. If seeds are left sitting on top of dry soil without being lightly covered, germination rates tend to suffer noticeably.
Are onions safe for pets?
Onions are toxic to dogs, cats, horses, and many other animals, with all parts of the plant posing a risk, including raw bulbs, cooked forms, and the green tops. Even small amounts consumed regularly can cause damage to red blood cells and lead to serious health problems. If you have pets that roam your garden, keep onion beds fenced or in areas the animals cannot reach.
What is the difference between long-day and short-day onions?
Long day onion varieties begin forming bulbs when daylight reaches roughly 14 to 16 hours, making them suited to northern gardens above about the 37th parallel where summer days are long. Short day onion varieties start bulbing with just 10 to 12 hours of light, which is why they perform well in southern regions where winters are mild and growers plant in fall. Planting the wrong type for your latitude typically results in either tiny bulbs or plants that bolt without forming a proper onion at all.
How do I know when my onions are ready to harvest?
The clearest signal that onion harvest time has arrived is when the green tops begin to yellow and fall over naturally, usually with half to two thirds of the plants showing this behavior before you act. At that point, stop irrigating and allow the bulbs to sit in dry soil for a few days if weather permits, which helps the outer skins start to firm up. After lifting, support the bulbs in a single layer in a warm, dry, well-ventilated spot out of direct sun for two to four weeks before you move them to long-term storage.