When to plant onion seeds

Wondering when to plant onion seeds? And how to grow them on? These seeds need to be planted early!

When to plant onion seeds

Onion seeds are generally planted in January or February. Most common varieties take about 90-120 days to grow from a seed to a mature onion, and so you need to plant them in late winter to harvest them by summer or fall. If you plant your onions late, you may not get a full-sized bulb and they may bolt, or go to seed, instead of producing a bulb.

Types of onion seeds to plant

There are several types of onions that can be grown, each with its own unique attributes:

  1. White onions: Mild in flavor, with a crisp texture. They are commonly used in Mexican cuisine.
  2. Yellow onions: Sweet and slightly tangy, with a firm texture. They are versatile and widely used in cooking.
  3. Red onions: Mildly sweet with a slightly sharp taste, they have a crisp texture and are often used raw in salads or as a topping for sandwiches.
  4. Spanish onions: Sweet with a delicate flavor and tender texture. Examples include Vidalia, Ailsa Craig, Kelsae and Walla Walla onions.
  5. Shallots: Mild and sweet, with a subtle garlic flavor. They are used in sauces and dressings.
  6. Pearl onions: Tiny and sweet, with a crisp texture. They are often used in stews, soups and pickles.
  7. Leeks: Mild and slightly sweet, with a tender texture. They are used in soups, stews, and as a garnish.
  8. Scallions (bunching onions, green onions): Mild and slightly sweet, with a crisp texture. They are often used raw in salads or as a garnish.
  9. Short Day onions: Gabriella these short-day onions are more suitable for growing in the south.

Starting onion seeds indoors

You will need:

  • Seedling heating mat
  • 1201 seed insert trays
  • Seed dispenser
  • Onion seed of your choice
  • Grow light
  • Good quality potting soil

Planting onion seeds (step by step)

Here are the steps to plant onion seeds:

  1. Fill each 1201 with soil to about 1/2 inch below the edge lightly packed.
  2. Moisten the soil lightly
  3. Place about 30 seeds in your seed dispenser
  4. Sow onion seeds about 30 seeds evenly into one 1201 insert
  5. Repeat this process with about 30 seeds in each until you have what you think you need.
  6. Place about 1/4 inch of soil over the seed and water in again.
  7. Place the 1201 packs on the heat pad
  8. Turn on the grow light as soon as you detect germination
  9. Use both bright light from a window as well as the grow light.
  10. When the onion seed germination is close to complete and the onions are about 1 inch tall remove them from the bottom heat.
  11. Start to fertilize with a water soluble feed 15-30-15 about once per week.
  12. Once the onion seedlings get about 3 to 4 inches tall trim them in half with household scissors.
  13. Let them grow back to about 3 inches tall again and cut them a second time. Once they get back to 3 to 4 inches tall you can cut them again if you feel they are not strong enough or just plant them out into the garden.
  14. When planting onion seedlings plant them about 1 inch deep about 4 to 6 inches apart and water well.

Direct seeding onions into outdoor garden soil

The process of planting onion seeds is as follows, if you live in a warm climate and can plant straight outside now (Mid-February) Zones 7-9 :

  1. Prepare the soil: Loosen the soil to a depth of 6-8 inches and mix in compost or well-rotted manure to improve fertility. Onions prefer well-drained soil with a pH of 6.0 to 6.5.
  2. Sow the seeds: Sow the seeds about 1/4 inch deep in rows about 12 inches apart, spacing the seeds about 1 inch apart in the row. Cover the seeds with soil and gently tamp them down.
  3. Water: Water the seeds gently after planting to settle the soil and keep the seeds moist.
  4. Germination: Onion seeds typically take 7 to 14 days to germinate. Keep the soil evenly moist but not waterlogged until the seeds have germinated.
  5. In cool weather pin clear poly to the surface of the soil over the seeds to get some heat to build up to speed up the process.
  6. Thin: Once the seedlings have emerged, thin them to about 4 inches apart. You can use the clippings in salads or as green onions.

Supplies you will need to direct sow onion seed into the garden in spring:

  • Onion seeds
  • Garden soil
  • Compost or well-rotted manure
  • Rake
  • Watering can
  • Garden gloves (optional)
  • Insect screen

Alternative- direct sow onion seeds in summer plan

Planting onion seeds around August 1st can result in seedlings that will overwinter and grow to size the following year. Onions are hardy plants and can tolerate cold temperatures, making them a good choice for overwintering. They should be the size of a small green onion by the fall. This seeding can be fairly dense in rows as you can lift them in the spring and replant them at an appropriate spacing then.

To get the best results, you should plant the seeds in a location that receives full sun exposure and has well-drained soil. As the seedlings grow, be sure to keep the soil moist and fertilize regularly to provide the necessary nutrients.

In the late fall, you can cover the seedlings with a layer of mulch or straw to help insulate the soil and protect the young plants from extremely cold temperatures. In the spring, remove the mulch to allow the plants to resume growth.

With proper care and attention, your onion seedlings should grow to a healthy size by the following July and be ready for harvest.

Growing Onion Sets (Onion Bulb)

Here are a few common types of onions that can be grown from sets:

  1. Yellow Onion: A sweet and mild variety that’s often used in cooking.
  2. Red Onion: A sweet and mild variety with reddish-purple skin and white flesh.
  3. White Onion: A sweet and mild variety with white skin and flesh.
  4. Shallot: A sweet and mild onion that grows in clusters and has reddish-brown skin.
  5. Multiplier Onion: Onion bulb that splits and multiplies
  6. Stuttgarter: One of the oldest onion sets.

Tips for growing onions from sets instead of seeds

These tips can help ensure that you get the best results from growing onions from sets.

  1. Choose a suitable location: Select a spot in the garden that has well-draining soil and receives adequate sunlight.
  2. Prepare the soil: Work compost or well-rotted manure into the soil to improve fertility and structure.
  3. Plant onion seedlings: When transplanting onion seedlings, gently remove sets from their containers and plant them at a depth of about one inch.
  4. Space sets according to the variety and the ultimate size of the plants, about 5 to 6 inches apart.
  5. Water onion sets well after planting.
  6. Protect your onion plants from insects: Cover the onion sets with insect-proof barriers such as floating row covers, mesh nets, or fine mesh screening to keep pests out. Reapply the cover after watering or when the weather turns windy. Another option is to use natural insecticides such as garlic spray, or pyrethrin.
  7. Mulch around the base of the plants to conserve moisture and suppress weeds.
  8. Harvest when the tops start to yellow and fall over, usually about 4 months after planting.


  • Onions are a cool-season crop and can tolerate some frost, but they grow best when temperatures are between 40-70°F.
  • If grown in the right conditions, onion seedlings should emerge within 2 weeks of planting and mature bulbs can be harvested after about 90-120 days.
  • You may have to protect young seedlings from pests such as onion maggots or thrips by covering the plants with insect screen.
  • With proper care, you can expect to harvest a good crop of flavorful, healthy onions.

When you are ready to grow onions these instructions should come in handy!

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