Onions are a staple in the kitchen as they truly bring food dishes to life. While they may be quite strong-smelling, onions are full of flavor, fairly cheap to buy, and versatile to cook with.

But, have you ever considered growing your own onions? Growing onions from seed takes patience. While some gardeners prefer to purchase immature onion bulbs, starting yours from seed can be done in just a few steps. Whether you plan to start your plant indoors or outdoors, this guide will help you learn how to grow onions from seed!

Materials Needed

Herbs seedlings growing in a biodegradable pots near garden tools on white wooden table. Indoor gardening, Homegrown plants, germinating herb seeds, close up

Image credits: Katrinshine via Shutterstock

Here is what you need to grow onions from seeds. Gather your materials and get to work!

  • Onion seeds
  • Seed starting mix
  • Seed tray or container
  • Trowel
  • Watering can
  • Gardening gloves
  • Grow light (optional)

How to Grow Onions From Seeds

planting seeds in containers

Image credits: Markus Spiske via Unsplash

There are two different ways to start your onion seeds; indoors and outdoors. Decide which method works best for you depending on your growing zone and climate. In general, plant onions outdoors four to six weeks before the last frost in your area. 

Of course, there are all different kinds of onions to pick from. Whether you enjoy red, Spanish, or yellow onions, with some TLC you'll have a bountiful harvest. Choose the variety you like the best and what would work best based on the climate you live in. You can purchase the seeds online or from your local garden center.

Types of Onions

different types of onions

Image credits: Sincerely Media via Unsplash

There are a few different types of onions that are referred to as short-day, long-day, and day-neutral onions. These terms are used to determine how many hours of sunlight an onion needs in order to develop its bulb.

Short-day onions start to produce a bulb when the plant receives 10 to 12 hours of sunlight per day. Grow this type of onion in zones 7 or higher as it requires a warmer, more mild climate. This type can also be started in the late fall for a harvest in the springtime. Short-day onions varieties include 'Yellow Granex,' 'Red Burgundy,' 'White Bermuda,' and 'Red Creole.'

Long-day onions need more time and sunlight to start developing their bulbs. They only start to produce a bulb when there is 14 to 16 hours of sunlight. This type of onion prefers a more cool climate and does best in growing zones 6 or lower. They won't tolerate warm temperatures, so make sure you are choosing the right type of onion for your climate. Popular varieties include, 'White Sweet Spanish,' 'Yellow Globe,' 'Red Wethersfield,' and 'Ailsa Craig.'

Day-neutral onions can handle a wide range of climates. This type of onion needs 12 to 14 hours of light per day to grow a bulb. They are typically planted in the fall and grown throughout the winter (depending on your growing zone) or in the early spring. Some day-neutral varieties include, 'Cabernet,' 'Super Star,' 'Red Stockton,' and 'Candy.'

Planting Onion Seeds Indoors

Person Planting Onion Herbs at Home in a Pot

Image credits: troyanphotos via Canva

Starting your seeds indoors requires a bit more effort, however, you can start the seeds much earlier than planting outdoors. Get a head start on the growing season by planting onion seeds indoors up to 10 weeks before the last frost date in your area, typically in February of March.

Step One - Plant Onion Seeds in a Container

To begin, choose which type of onion seeds you'd like to grow and plant them in a small container with drainage holes. Fill the container or seed tray with seed-starting mix and water thoroughly. Plant multiple seeds per container, 1/4 inch deep, and cover with soil.

Step Three - Wait for the Seeds to Germinate

Onion seeds will take anywhere from four to 10 days to germinate. The ideal soil temperature for germination is 50 degrees Fahrenheit. While waiting for the seeds to germinate and sprout, make sure to keep the soil evenly moist. Water your growing onions at least once a week.

Step Four - Place Seedlings Under a Grow Light

Once the seeds have germinated, you can then place them under a grow light. Typically, seedlings need 14 to 16 hours of light per day so you'll need to supplement with artificial lighting.

Step Five - Harden Off Seedlings  

Before transferring your onions outdoors, you need to do a process referred to as hardening off. Place the seedlings outdoors for a few hours a day to get the plants used to their new environment. Continue this for a few days, gradually increasing the amount of time each day. Doing this process allows your plant to become adjusted to the outdoor elements.

Step Six - Plant Seedlings in the Ground 

After four to five weeks of growing indoors, you can finally plant your seedlings outdoors. It's best to get them in the ground right before the last frost. When transferring to your garden, plant the seedlings at least 6 inches apart and water thoroughly. Choose a location in the garden that is free from any weeds and receives lots of sunlight.

Planting Onion Seeds Outdoors

planting onions in the garden

Image credits:

Markus Spiske via Unsplash

If you decide to plant your onion seeds outdoors, it's important to start at the right time. Always check the frost date for your area first and begin planting in the early springtime. The earlier the better, as the cooler weather promotes leaf growth in the beginning stages of development.

If your climate tolerates it, you can start planting onions in late winter, from December to February. Onions are cool-season crops and can tolerate a light frost, so make sure to plant your seeds as early as you can in the garden so they can establish themselves.

Step One - Drop Them in the Ground

Start by deciding on an appropriate location in your garden or a container. Depending on the type, onions need anywhere from 10 to 16 hours of sunlight per day, so plant them in an area of your yard where they'll be happy in the sun. Plant the seeds in rows, 6 inches apart and 1/4 inch deep. Ensure you place a few seeds per hole to ensure germination.

Step Two - Wait for the Seeds to Germinate

Onion seeds take anywhere from four to 10 days to germinate. When planting in soil outdoors, the seeds remain dormant until the right soil temperature is reached. Generally, onion seeds will germinate when the soil temperature is 50 degrees Fahrenheit. Seedlings grown outside like this will sprout when the time is right.

Step Three - Water and Check on Seedlings

After the seeds have germinated, check on the plants regularly. Water often and don't let the soil dry out, about 1 inch of water per square foot every week. Since there are multiple seeds planted, thin out your seedlings to prevent overcrowding. Only keep the ones that are growing strong and healthy.

Step Four - Fertilize Regularly

Onions are heavy feeders and should be fertilized every few weeks. As your onions grow, you may notice the bulbs starting to grow out of the soil. This is completely normal and you shouldn't try to force or push the bulbs back into the soil. Stop fertilizing your onions when the bulbs start to emerge from the soil.

Harvest Time

Spring onions in pot

Image credits: Studio_Loona via Shutterstock

You'll know your onions are ready for harvest when the tops look dry and start to fall over. Once this happens allow the crop to tip over and halt water for about a week. This will ensure that the plant is dried out and the skin has toughened. Remove the excess dirt and you're done!

Grow Your Own

Follow these steps and consider growing onions in your backyard garden next. With regular care and the right growing conditions, you'll be harvesting lots of homegrown onions in no time at all!

Have you tried growing onions from seed before? Leave a comment down below.