Growing Onions from Seed

Onions are a must have in many kitchens. They’re easy to grow from seed and many gardeners start them indoors before the last frost in order to have a jump start on the gardening season. Onion seeds do very well in any seed starting mix.

onions growing photo


Fresh Seeds

Always start with fresh seeds. You can keep seeds stored for up to two years in a cool and dry place. However, keep in mind that first year seeds will do the best for germination.

Once you’ve chosen your fresh seeds and your new potting mix, you’ll want to choose where to start your seeds. You’ll want to start your seeds about 10 weeks before you plan to put them outdoors in the garden so you’ll want an area that won’t be in the way for your seeds to sit and germinate.

Bottom Heat

Onion seedlings do best with a bottom heat so you’ll want to plan on using some sort of florescent plant lights that are flat and will give off enough heat to help your seeds germinate. The ideal temperature for onion seeds to germinate is 65 to 77 degrees Fahrenheit or 20 to 25 degrees Celsius. The temperature can be slightly lower at night.

Many gardeners find that the top of the refrigerator is an ideal location to give the onion seeds just enough heat and they are out of the way.

Planting The Seeds

Place your soil into the containers (you can use recycled containers, paper cups or anything else that you desire for your containers but most gardeners prefer something that they can simply set into the ground so paper is usually best) that your seeds are going to be planted in.

After you’ve placed the soil into the containers, you’re ready to plant your seeds. Place several seeds in each cup or general area and lightly press them into the soil. Don’t press them in too far.

onions growing photo


After your seeds germinate, the husk may not completely come off of the seed. This may look like a small green loop. To speed the process up, gently snip the loop in half and pull on the small end. Toss this end away.

Once your seedlings have emerged, you’ll want to place them under a brighter light. You can use two florescent bulbs or something similar. Keep the light on the onions for up to 12 hours per day. They should be within about an inch of the bulbs. Each day trim the onions back so that they are about 3 inches tall. This will prevent them from falling over. You can use scissors for this.


Transplant when there are three leaves. When the seedling has its first three leaves, it’s time to transplant them into new containers. Again, use recycled materials. Most gardeners use the bottom half of a cardboard milk carton for this. It offers plenty of depth and width and you can simply cut the bottom off of them when you put them outdoors.

Shortly after transplanting the seedlings, your onion seedlings are going to shed their seedling leaves. Allow these to fall off or snip them as they die off and toss away. Once transplanted your seedlings are going to take off on a huge vertical growth spurt. Keep trimming these back to 5 inches for now.

Offer Light

Offer your seedlings plenty of light, they will thrive in the light. Either place them near a sunny window or move them outdoors during the day when the sun is out. Shield them from the wind to protect them.

onions growing photo

Hardening Your Seedlings Off

Once temperatures level off to about 50 degrees Fahrenheit or 10 Celsius, your seedlings are ready to harden off and begin leaving out longer and longer. You want the temperatures to be leveled off and slowly climbing or your seedlings will bolt and they won’t produce bulbs.

Fertilizing Your Onions

When you prepare your planting area, you will want to make the trenches and then line them with a rich compost or an organic fertilizer. This will leave a vault of nutrients in the soil so that your onion bulbs will have plenty to eat. They’ll use it during their active growth period.

Weed Suppression

Once your seedlings are safely in the ground, it’s time to plant some rows of leafy greens in between them, this will help to battle the war against weeds. Consider such leafy greens as arugula, spinach, lettuces and similar leafy greens. Salad greens work very well to smother weeds in between onions.

Your onions will be ready to pull up in the late fall. When they begin to develop a “bulb” on top they are usually near ready. Dig one or two up to see how large they are. You’ll enjoy your onions for the rest of the season.

You can trim the greens and eat them or dry them and use them throughout the year. Allow the bulbs to dry out and gently shake or wipe the dirt off of them. Turn them over in the sun for a day or so to allow them to dry completely before storing them in a cool dark place for the winter months.

To use, simply peel off a few layers and slice your onions as desired. Enjoy cooked or raw.

Growing onions from seed might sound like hard work, but it has a distinct number of benefits for gardeners and vegetable growers. Find out how to grow onions from seed in this detailed guide from an experienced British vegetable grower.

Photos c/o USDAgov, & USDAgov