How to grow onions from seed

Onions are a must have on our homestead. Whether it’s onion powder, fresh, frozen, or dehydrated they are definitely used daily. This year I am growing onions from seed instead of the sets from the store (actually, I am going to grow both and see which grows better). I thought I would take you all along with me! I’m excited to give it a try! Let’s talk about how to grow onions from seed.

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What type of onions should you grow

First, know your growing zone to determine what type of onion will do well in your climate.

Long day: Long day onions require 14+ hours of daylight a day to form a bulb. Long day onions are best grown in norther regions. Plant them in the late winter or early spring. Good Storage onions. Examples are Walla Walla, Copra, Yellow/White Spanish. 90 days to maturity.

Short Day: Short day onions require 10-12 hours of daylight to form bulbs. Good for Zone 7 or warmer. Plant them in the fall and will be ready to harvest in the spring. Examples are Red Ceole, Vidalias, Snowball White. 110 days to maturity.

Day-Neutral: Day-Neutral onions require 12-14 hours of daylight to form bulbs. Good for zone 5-6. Plant late fall or early winter. Examples are Candy, Sweet Red, Cimarron. 110 days to maturity.

You begin counting days to maturity the day you plant the seedling in the outside garden not when you plant the seed.

What you need:

Potting soil–I use whatever is available at my local garden center.

onion seeds: check out Bakercreek seeds or Southern Seed Exchange. I am not affiliated with either company, I have used their seeds and they have been excellent quality.

grow light set up: click on the link for a post on starting your seeds under grow lights and what we use for that set up.

seed starting trays: I use the 72 cell trays you can find in the garden center at Lowes or Walmart, or you can use just the tray part filled with dirt.

Let’s Plant Together

Start by preparing your potting soil by mixing water and soil together until the soil holds together when you squeeze it. Fill the tray cells with the soil.

Sprinkle the seeds onto the soil covering them with 1/4inch of soil.

grow onions from seeds

Mist the soil with water and place the lid on your seed trays so that everything will stay moist. Check on them periodically to make sure that the soil does not dry out. Check out my favorite sprayer for keeping the seedlings wet.


Onion seeds do not need light to germinate. So, I set my tray on the top of my shelf away from the direct light.

Once the seeds are germinated place them under the grow lights. I am growing long day onions so I will leave the lights on for 11-12 hours and then shut them off. I’m not really sure grow lights have enough power to stimulate bulb production BUT just in case I am monitoring the amount of light the onions receive.


The onions sprouts will grow green shoots and will become unruly and tangled if left to grow. Keep the onion tops trimmed to about three inches high until you transplant them out into the garden.

By the way don’t throw away the onion pieces you just trimmed off. They are delicious! Cut them up and sprinkle on a baked potato, a salad, or on scrambled eggs!

How to Harden Off?

Before planting your onion starts in the garden outdoors it is imperative to harden off your plants. The onions cannot handle the full strength of the sun right away and will die.

Start by sitting the plants in a shaded area outside for about 30 minutes. Bring the plants back inside and make sure they have plenty of water. Repeat the process the next day increasing the time to an hour.

After several days of handling the shade, place the onions in direct sunlight for about 30 minutes. Increase the time daily until your plants can handle all day. Leave the plants outside all day and all night the last two days before transplanting.

When Are My onion plants Big Enough to Transplant?

Transplant the onion seedlings when they are 5-8 inches tall and have three or more leaves and when temperatures outdoors are no longer dipping below 28 degrees.

You did it! It’s time to plant your onions in the garden!

Other Post you may enjoy:

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Why We Choose to Homestead

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