How to Grow Green Onions (Allium cepa)

By Erin Marissa Russell

If you’ve been considering growing some green onions, we’ve got all the info you need to choose the right variety for your garden and raise a bumper crop of these tasty little vegetables. Get ready to learn all about how to plant bunching onions, how to take care of them once they sprout, and how to harvest, propagate, and store them.

We’ll even talk about the characteristics of different species as well as common pests and diseases that can strike a crop of bunching onions. If you’ve got questions, they’re sure to be answered here, so just keep reading to become an expert on growing bunching onions.

Humans have been growing onions as a food crop for literally millenia. We’ve been cultivating onions for more than 4,000 years—that’s before the advent of recorded history. Experts believe that onions are most likely native to either Asia or the Mediterranean, but they’ve been used in cuisine in both China and India for a very long time as well. Humans have seen onions as more than simply a food source, too.

Before Christianity began, onions were actually worshiped in Egypt, and across the sea in Britain, they played a role in the rituals of druids, who took vows with one hand on an onion, much like modern people swear an oath while touching a Bible. Both the druids and the Egyptians found spiritual value in onions because of their layers of concentric rings, which reminded these ancient people of eternity and the nature of the universe, continually unfolding in a cycle. Some cultures associated onions with evil, while others associated them with protection from evil. These days, we tend to associate them with the delicious flavor we’ve come to love sliced over chili, sprinkled on baked potatoes, and topping the melted cheese on our nachos.

Growing Conditions for Green Onions

You’ll see onions referred to as short day, long day, or day neutral, according to how many hours of sunlight they need to bulb. For day neutral onions, it doesn’t matter. Long day onions need 14 or 15 hours of sunshine to grow bulbs, and short day onions need 10 hours of daylight. However, this won’t come into play with green onions because you aren’t growing them for their bulbs as much as for the long, green tops that grow above the ground, which need just six hours of daylight to do their growing.

Green onions need a soil that drains quickly and won’t hold too much water when it rains, even when the weather is cool, since green onions grow best when the temperature is between 68 and 77 degrees. You can improve your soil before planting green onions by mixing in two or three inches of well-rotted compost.

Other than the need for good drainage, green onions aren’t particular about the type of soil they grow in. That said, you should avoid planting green onions in soil that’s overly acidic. They do best when the pH level of the soil is between 6.2 and 6.8. (Not sure what the pH level of your soil is? You can find out by reading our article How to Test pH in Your Soil.)

It’s best to practice crop rotation and grow your green onions in a plot where alliums haven’t been grown for at least three years. Doing so will prevent a lot of the soilborne diseases that can plague allium crops.

How to Plant Green Onions

If you’re growing regular bulbing onions, you can use the plants you pull up when thinning out your onions as green onions. But that’s only one way to get green onions. Here’s how to grow them specifically to be used as green onions.

As soon as the soil can be worked in spring, it’s time to plant your green onion seeds. Green onions will sprout as long as the soil is anywhere between 65 and 86 degrees. Seeds should be spaced an inch to an inch and a half apart and covered with half an inch of soil, while sets can be placed two inches apart. If you want, you can start your green onions indoors six to eight weeks before planting them. Water the soil after planting, and keep it consistently moist while the seeds sprout and when plants are young.

Care for Green Onions

You’ll need to water your onions regularly as they grow in order for them to grow healthy and strong. Water deeply, down to a depth of 18 inches, every 7 days. Water is especially important for onions because of their shallow root systems. If they don’t get enough water, you’ll see a smaller harvest, smaller bulbs, and less tasty onions.

In the first two months of growth for your green onions, you’ll need to weed their plot religiously. The plants will be growing slowly and won’t be able to compete with the invasive weeds. You can make your job easier by mulching the area with compost, grass clippings, or leaves to smother any weeds that would otherwise come up.

You can help your green onion plants to develop long, white stems by pulling an inch or less of loose soil up around the plants once they’ve reached a height of five or six inches. Should you need to transplant your green onions to another area, cut their roots in half first.

How to Propagate Bunching Onions

You can grow green onions from seeds, sets, or even from scraps. Sets are simply small bulbs or young plants that you can transplant into your garden. To grow green onions from scraps, reserve the root end of the plant with a bit of the bulb attached to it, and set this end in a sunny windowsill in a container of water. It will regenerate more green tops for you to use.

Garden Pests and Diseases of Bunching Onions and Scallions

Onion plants are resistant to deer and rodent problems, as these animals don’t like the sulfrous taste of the part of the onion that grows above ground. The most common problems are onion thrips and onion maggots.

Allium leaf miners: Leaf miners cut tunnels in the greenery of plants as larvae feed on them. Learn how to fight them by reading our article on the topic here.

Allium rust: Allium rust is a fungal disease that creates orange pustules on the leaves, causing them to turn yellow and die. Infected plants must be removed and destroyed. Do not plant alliums in an area stricken with allium rust for at least two or three years.

Armyworms: Learn about the different kinds of armyworms and what you can do against them in our article How to Get Rid of Armyworms.

Damping off: Damping off strikes during the seedling stage, causing baby plants to wither and die. Learn more in our article How to Prevent Damping Off.

Downy mildew: Downy mildew is a fungal disease perpetuated in wet conditions. Learn more in our article on identifying, preventing, and treating downy mildew.

Onion maggot: Onion maggots are the larvae of a small, gray fly. If they are infesting your crop, you may notice poor sprouting or survival of young plants or yellowed, limp foliage once plants grow older. Rotating crops is vital to prevent infestation. Also ensure compost is completely rotted before using it in the garden.

Onion thrips: Tiny onion thrips tend to feed in the areas down between the blades of onion leaves. Check this area deep inside the plant for the yellow juveniles or darker colored adults. You can fight them with predatory lacewings, pirate bugs, or other thrips. Prevent them by making sure to clean the field well at the end of each season so they don’t have a place to hide. Straw mulch can also help prevent their infestation.

How to Harvest Green Onions

Green onions can be harvested as soon as 40 to 50 days after seeds are planted or 30 days after sets or transplants are placed in the garden. They’re ready when the tops have grown to six inches tall and are as big around as a pencil. The older and larger green onions grow, the stronger their flavor will be. If they get too strong to be eaten raw, you can always cook with them. Harvest by simply pulling them up gently.

How to Store Green Onions

Store your green onions in the garden when appropriate, or they will keep in the refrigerator for about a week in a plastic bag with a damp paper towel. Do not consume shriveled or yellowed leaves; pull these off before eating or preparing green onions.

Green onions are set on the table raw and whole in the soul food tradition and on tables in the American South. They’re also often used raw, sliced into thin circles.

Here’s a video from Purdue on how to slice them.

You’ll also see them sauteed in recipes, especially the white portion. Sometimes, green onions are grilled either whole or cut into halves. However you prepare them, homegrown green onions are so much tastier than store bought, and they’re easy to grow, too. Find out for yourself and plant some green onions in your garden next season.