The name green onion refers to many different types of onions. Learning how to grow green onions ensures you’ll always have access to the freshest, most flavorful alliums you can find!
The true green onion is Allium fistulosum, also known as scallions, bunching onions, or just plain old green onions. These are the ones we’ll focus most of our attention on today.
Traditional onions, Allium cepa, have a red or white bulb, but they can be harvested before the bulbs form, and the young stalks can be used like green onions. Finally, there is Allium proliferum, called tree onions or Egyptian onions. These onions are harvested specifically for their long green leaves. They develop in tight knots of multiple bulbs and stems attached together, and tend to spread over time.
If you’re wondering how to get all of these delicious varieties of green onions, we have tons of information to share! We will go over how to start green onions from seeds, starts, or other methods. Let’s jump into how to plant green onion seedlings in your garden.
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Quick Care Guide
|Common Name(s)||Green onion, scallion, Japanese bunching onion, Welsh onion|
|Scientific Name||Allium fistulosum|
|Days to Harvest||60-95 days|
|Light||Full sun, around 8 hours|
|Water||1 inch per week|
|Soil||Fluffy and neutral, pH between 6.0 and 7.0|
|Fertilizer||Balanced, can amend with organic matter|
|Pests||Aphids, onion maggots, slugs, snails, thrips|
|Diseases||White rot, onion downy mildew, leaf blight|
All About Scallions
Allium fistulosum, or green onions, are also commonly called bunching onions, scallions, Welsh onions, or Japanese bunching onions. It is likely that they were foraged in the wild before becoming popular in China and Egypt. Tokyo Long White, Evergreen, and Heshiko are some of the most popular varieties.
Green onions look similar to the traditional onion, Allium cepa. They have tall, green stalks, and are usually 1-2 feet tall. They have slender white bulbs at their base that do not get large enough to form an onion. In hot temperatures, scallions will bolt to seed, forming a globe shape of tiny white flowers.
Green onions are perennial and the scallion leaves can be harvested for several years in mild climates. All parts of scallions are edible, including the flowers. Thinner scallions will have a milder taste, while thicker onions will have a stronger flavor and hold up to cooking better.
One interesting fact about scallions is that you can tell the variety by looking at a cross-section of the leaves where they turn white: if it is D shaped or flat, it is A. cepa, but if it is O shaped, it is A. fistulousum.
Planting Green Onions
Begin to sow seed indoors 8 to 10 weeks before the last frost. Keep the seeds moist and they should emerge in 7 to 14 days. If direct sowing seed, sow each seed ¼ inch deep when temperatures are at least 50 degrees Fahrenheit. A seedling heating mat can help with germination. Thin seedlings so they are 2 inches apart or leave them to separate later.
When the seedlings are ready to transplant, separate the seedlings. Begin to transplant 2 to 4 weeks before your last frost date in the spring, but if desired you can keep planting throughout the spring and summer season and into the fall. Space seedlings one to two inches apart, with rows spaced 6 inches apart. Consider interplanting with your other crops as green onions may help to repel pests from your garden. Be sure to irrigate regularly as onion plants have shallow roots.
Plant traditional onion sets 2 to 4 weeks before the last frost date. Care for them like you would a transplanted green onion, but plant at least 2 inches apart to allow space for bulb growth. Remember, the green leaves can be used just like green onions are, but an Allium cepa will eventually form a larger onion bulb.
Now that you know more about the types of green onions, let’s learn how to take care of them so they can mature! Let’s go over more of the specifics on how to care for scallions.
Sun and Temperature
Plant in a sunny location that gets at least 6 hours of full sun. Scallions form best in zones 6-9 and thrive in temperatures between 60-75 degrees Fahrenheit. If you plan to grow scallions through the winter, mulch around your planted bulbs in the fall with straw or other organic matter to protect them from cold temperatures and prevent weeds.
In zones warmer than 9, you might want to plant your green onions somewhere in the garden where they will receive afternoon shade. Since onions like full sun, it is definitely possible to raise scallions in hot climates!
Growing green onions indoors is also an option, particularly for those who have cold winters. Make sure they have plenty of light and warmth during the cold season and you’ll have scallion harvests through the winter and well into the spring.
Water and Humidity
Morning is the best time to water to reduce soil moisture evaporation. This also allows foliage to dry out during the day so they’re less prone to disease.
Scallions are sensitive to drought. Aim for 1 inch of water per week. Use soaker hoses or drip irrigation. Ditch or “furrow” irrigation is another viable method. Dig a long trench in the soil an inch or two from your plants and flood the furrow, allowing the bulbs to absorb moisture.
If you have sandy soil, you will need to irrigate more frequently. In a cooler season or mild climate conditions plants develop more slowly, so less watering is required.
Scallions prefer fluffy, well-balanced, and loamy soil. If you have poor soil, amend it with organic matter like compost at least six inches deep. While onion bulbs are able to develop in clay soil, they have a hard time if it dries out, and the soil may hold a little too much moisture for their liking. It’s best to amend to allow for good drainage while still keeping the soil moist.
To grow scallions, the optimal soil pH range is between 6.0 and 7.0. These bulbs can tolerate soil pH a little lower than 6.0, so if you’re planting them near tomatoes or other solanaceous plants, they’ll manage. If soil is too alkaline, these may struggle to get off to a good start.
Since scallion plants are leafy greens, you’ll want to fertilize them every regularly with a nitrogen-rich amendment. Liquid fertilizers such as fish fertilizer or comfrey tea have nutrients immediately available to your plants, so consider watering with a liquid fertilizer during the growing season to provide nutrients when your plants need them most. For a longer-term solution, use granular fertilizers that will be released slowly into the soil. Look for one that is high in nitrogen (the “N” in N-P-K). If desired, top-dress with rich compost.
Most of the time, pruning is only done for harvesting purposes. Plants can be trimmed for cosmetic purposes, such as removal of wilted leaves, but otherwise should be left until it’s time to pick them.
If your green onions bolt to seed and you want to prevent seed drop, trim off the flower stalk. Often, you may experience leaf wilt during flowering as well. Early trimming of the bud and stalk (referred to as an onion scape) will redirect your plant’s energy towards leaf development.
If you’d like to collect seed, let the flowers fully open. Onion flowers are pretty impressive. They create a large, almost ball-shaped umbel. As the flowers start to fade, tie a paper bag over the top and tightly secure it to the stalk. The seeds are very tiny. Cut the stalk once it begins to droop, and set it somewhere so that the head can dry out and the seeds can drop out of the flower.
One method of propagation is bulbs or “sets”. The best way to use sets is by planting them in late fall and overwintering them in the garden. In the spring they’ll start pushing up new growth.
You can also use nursery starts of Allium cepa, and plant them to achieve the green onion stalks. Keep in mind that only Allium fistulosum will produce tree green onions with no onion bulb. True scallions have a milder flavor than A. cepa, which has a stronger onion flavor.
If you save rooted bulbs from store-bought green onion plants, you can easily regrow green onions. They’ll happily produce tall, green leaves every couple of weeks and give you a bonus crop. This works both indoors and outdoors, so if you’d like to save your young green onion bases from the supermarket and pop them into moist soil under a T5 light, you’ll see new growth rapidly emerge!
And, of course, starting from seeds is definitely an option. There’s a wide variety of seeds available for many different species of scallion or bunching onion types. Follow the directions in the “planting” section above for how to sow seed.
Harvesting and Storing
Wondering what to do once you have mature green onions? Let’s talk about how to harvest the plant and what to do with your delicious scallions!
Start to pick your green onions as soon as they reach a usable size. The best time to harvest is when the bulbs are white and have a diameter about the size of a pencil, but even smaller seedlings can be harvested. In fact, it’s possible to sow onion seeds and harvest onions as microgreens if you so choose!
Either dig up the whole plant if you plan to eat the mild white bulb, or snip the stem off just above soil level and allow it to continue growing. A clean pair of kitchen scissors or garden snips work well for this. Cut-and-come-again harvests like the latter method mean you can enjoy a continual harvest by leaving the roots and base of the plant in the ground and cutting the stalks off an inch or two above the soil line. The plant will quickly send up more edible shoots!
When growing traditional bulb onions as green onions, harvest the green leaves early and use them like scallions. Egyptian onions should be harvested from the second season onward.
If your plant is bolting, the stalk and unopened bud are referred to as an onion scape. Onion scapes are just as delicious as the leaves are, and can make an incredible addition to a stir-fry or other meal.
Store green onions in a partially filled jar in your fridge, with just enough moisture to come partway up the bulbs. If you harvest stalks without bulbs, store the stalks wrapped in a paper towel in a plastic storage bag. Alternatively, slice them and refrigerate them cut, also in a plastic bag. Moisture is the enemy to your green onions as they’re being stored with these methods, so the paper towel is crucial to keep bulbs and leaves dry.
To freeze green onions, rinse them off and thoroughly pat or air dry them before freezing. The texture will often be a bit mushy when they thaw out, so this is best if you plan to use them in cooked food rather than as a garnish
If you have a dehydrator, dehydrating the stalks and grinding them into a powder is a great option for long-term storage.
Now let’s discuss some problems you might encounter while growing scallions. Since scallions are in the Allium family, they tend to repel many pests with their odor, although they are susceptible to a few pests and diseases that are easily treatable.
Too much moisture can cause your growing scallions to develop some forms of root rot. Be careful to provide just enough moisture for them to thrive. Use a drip hose or other irrigation system to keep the soil damp. On the flip side of that, too little moisture causes leaf wilt or yellowing, so make sure they aren’t thirsty.
If it is too hot, your onions will bolt to flower. Be careful to plant them at the right time for your growing zone.
Competition from weeds can cause scallions to be small and weak or even die. Check your plants regularly and pull any weeds out from around them, especially ones in their root zone. Mulching can reduce weeds as well.
Thrips and aphids are common pests in onion crops and can be blasted off with a strong stream of water from a hose. If they persist, use insecticidal soap or neem oil. Severe infestations can be treated with pyrethrin.
Onion maggots can be prevented by following crop rotation in the garden. You can also use floating row covers as a barrier against the flies that lay onion maggot eggs. Beneficial nematodes are natural predators of onion maggots. Most pyrethrin insecticides that work on thrips will also help manage onion maggots.
Slugs and snails are also an issue, but they’re easy to treat. A beer trap can be placed amongst your crops to catch some of these annoying pests. As long as it’s about as deep as a pie pan, snails and slugs will be attracted to the aroma of the beer and it’ll be deep enough to drown them. If you don’t want to use beer traps, an organic slug and snail bait is another great option and will draw the pests away from your greens.
White rot can cause mold or rot at the base of the plant and yellowed, wilted leaves. If you notice diseased plants, remove and dispose of them. Avoid planting alliums in that location for a couple of years. Good crop rotation is essential for your allium’s health.
Onion downy mildew (Peronospora destructor) can cause irregular spotting and decreased size. Copper fungicides can be used to treat, but use a 3-year crop rotation between allium crops in that bed.
Botrytis leaf blight causes white spots on leaves, and the plant may wilt and die. This is most common when plants are wet for 20 hours or more during cool temperature conditions. Provide proper airflow to allow plants to dry out. Treat with alternating copper and sulfur fungicides until the blight is eliminated, or remove infected plants and destroy them. Do not compost blighted material.
Frequently Asked Questions
Q: Do green onions grow better in water or soil?
A: Although you can temporarily regrow green onions in water, the roots won’t have any nutrients or oxygen to survive long-term. Soil will provide the nutrients they need.
Q: Do green onions grow back every year?
A: Green onions are biennial and can live for several seasons. They will come back after being cut down, but they won’t regrow if the bulbs die or are frozen.
Q: Do green onions die in the winter?
A: Some varieties can tolerate frost, although they won’t survive sustained periods below freezing.
Q: Do green onions tolerate heat?
A: Yes! They do well in warm climates with humidity, although they will eventually bolt and go to seed.