Onions will sprout sooner or later – it is nothing to worry about. Still, you have to decide if you want to throw them away … or do something else (like plant them and see what happens!)
So, can you plant onions that have sprouted? You can plant sprouted onions – but if you plant the whole bulb, you will get several smaller onions. To get larger onions, separate the onion, then plant the sections apart to give them room to grow. You can also harvest seeds from the flowers that grow on the stalk of an onion in its 2nd year.
The key thing to know: a planted 2nd-year onion is not the same as a first-year onion grown from seed. When you plant a sprouted onion, you won’t get a large globe-like onion like the ones you get when planting from seed.
But you can turn one large sprouted onion into several smaller ones over the course of a growing season – and maybe get some onion greens and seeds out of it too.
In this article, we’ll explain how to plant a sprouted onion. We’ll also get into why onions sprout and how their life cycle works.
Let’s get started. And no crying over cut onions!
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Can You Plant Onions That Have Sprouted?
You can plant onions that have sprouted to get more onions. But these new onions will be smaller than a full-grown onion grown from seed.
When the green leaves on top of the onion get big enough, you can harvest those for onion greens. Chop up the leaves and use them for cooking to add nice onion flavor to a dish.
Planting the entire undivided onion might not work so well. First of all, there are different types of onions, and each grows best in different regions:
- Short-day onions will start to form a bulb when there are 10 to 12 hours of daylight. They are suited for southern latitudes.
- Intermediate-day onions will start to form a bulb when there are 12 to 14 hours of daylight. They are suited for middle latitudes.
- Long-day onions will start to form a bulb when there are 14 to 16 hours of daylight in a day. They are suited for northern latitudes.
For example, if you live in a northern latitude and bought onions grown in a southern latitude, you might not have as much luck growing new plants. At the very least, the bulbs will not grow to their full potential.
If the onion is old enough, it will start to rot inside. If you plant the rotten part of an onion, the rest of the flesh will rot in wet soil. In that case, you won’t get anything for your planting efforts.
So, what should you do instead?
How Do You Plant An Onion That Has Sprouted?
For best results when planting a sprouted onion, follow these steps.
Step 1: Remove The Skin & Separate The Onion Into Sections
First, take your sprouted onion and remove the papery skin. Do it just like you would remove the skin before chopping an onion for cooking.
Next, start to peel back layers of the onion (the white, yellow, or red flesh), one layer at a time. When peeling, be careful not to damage any healthy green leaves growing at the top of the onion.
If some of those leaves are brown or black, just cut them off and throw them away. Also, be careful not to damage any new roots growing at the bottom of the onion.
These new roots will be thin and white. They will help the onion to grow after you plant it.
Keep peeling back layers of the onion. Eventually, you will see one or more sprouts bunched together at the center of the onion.
Separate the sprouts, using a knife to cut and divide the root portion at the bottom. Make sure that each sprout gets some of the roots.
Step 2: Soak The Sprouts To Grow Larger Roots
If the onion has been sprouting for a while, the roots on the bottom will be long. If the onion has just started to sprout, the roots will be small and weak.
In that case, you can soak the sprouts in water to encourage root growth.
First, find a small container that will hold all of the sprouts. Put some water in the container – enough so that the roots are in the water and able to absorb it.
(The water only needs to be deep enough to cover the roots and a little bit of the sprout at the bottom).
Next, put the sprouts in the container. Make sure that the roots have access to the water.
Then, put the container in a place where it will get plenty of sunlight (a windowsill is good). You can also use a grow light if you want.
Change the water every day or two to keep it fresh. When you see white roots at the bottom of the sprout growing longer underwater, you will know it is working.
(Note: this root-growing process might take a week or more).
Step 3: Transplant The Sprouts
Now that your onion sprouts have stronger roots, they are more established and ready to move into soil. Don’t wait too long to transplant them, since water alone will not provide the nutrients the onion needs to grow.
Before transplanting, make sure to mix some compost or aged manure into your garden soil. This adds nutrients for the plant, along with organic material that attracts beneficial soil organisms (such as earthworms and bacteria).
(You can learn how to make your own compost in my article here).
Compost is even more important if you have clay soil, which drains poorly. Onions like well-draining soil, and adding compost to the soil will improve drainage.
(If your soil drains poorly, you can learn how to fix it in this article).
When you transplant the onion sprouts into the garden, bury each one in the soil so that only the green part of the plant is above ground. Leave 4 to 6 inches (10 to 15 centimeters) between onions.
This will allow room for them to grow and “bulb up”. It will also prevent competition between nearby plants.
(You can learn more about onion depth and spacing here.)
Water them well, and keep the soil moist (but not soaking wet).
Step 4: Harvest
The onion sprouts will get larger throughout the growing season. However, they won’t get as large as onions that you start from seed.
When the green onion leaves above ground start to fall over, it is close to harvest time. At harvest, you should expect an onion with more of a tall oval shape, rather than a large spherical bulb shape.
These onions will not be as large as onions grown from seed. (You can learn more about just how big onions will get in this article).
You can also learn how to make onions grow larger (and how to care for them) in this article.
If you want to get seeds from your onions, just let them keep growing instead of harvesting them. Eventually, the onion plant will send up a tall stalk.
Next, a flower (often white or purple) will grow at the end of the stalk. Then, black seeds will appear on the flower stalk.
If your onion plants start to flower and produce seeds sooner than you would like, there is not much you can do. According to the Texas A&M University Extension, an onion that flowers and produce seeds will produce smaller bulbs (since some of its energy is going to flower and seed production).
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Why Do Onions Sprout?
Onions, like any other plant, want to reproduce and create the next generation to follow them. Even in hostile conditions, they will try to do this.
Sprouting is the first step in this process for an onion in your cupboard. Note that long-day onions store best, and onions that have grown to full maturity (but without seed stalks) will store longer.
Onions are biennial plants, which means that they take two years to complete their life cycle. You can plant onions from seeds, sets, or transplants.
The onion plant grows during spring and summer. When a large bulb forms and the green leaves fall over, the onion is ready for harvest.
However, if you leave the onion bulb in the ground over the winter, the plant will continue with the second part of its life cycle. The top of the bulb will sprout, and it will try to produce flowers and seeds in the spring.
These seeds will then grow into the next generation of onion plants, and the cycle continues! You can see the life cycle of an onion illustrated below.
Onions use some of the nutrients and sugar in their flesh to create new green growth (sprouts) at the top of the onion. A sprouted onion will also start to send out roots from the bottom as it seeks out soil to grow in.
With the right conditions, an onion plant will send up a tall stalk that will flower and produce seeds. Some of these seeds will grow in the soil, start new onion plants, and begin the cycle again.
To prevent sprouting, first make sure to “cure” your home grown onions by leaving them out to dry. Once cured, store the onions in a cool, dry, dark place to slow down the sprouting process.
On the other hand, if you want to try planting sprouted onions, there is a way to speed up the sprouting process.
How To Make Onions Sprout Faster
If you want to make your onions sprout faster, first give them light and heat. Onions stored in cool, dry dark conditions will not sprout as fast.
Also, store your onions with other fruits or vegetables that give off ethylene gas. According to the University of Vermont Extension, apples and tomatoes give off ethylene gas, which causes onions to sprout faster.
According to the Iowa State University Extension, bananas and potatoes also give off ethylene gas.
Are Onion Sprouts The Same As Green Onions?
Onion sprouts are not the same as green onions. In fact, the wording can be pretty confusing.
Let’s try to clear things up by listing the types of onions in order from youngest to oldest:
- Onion sprouts are the seedlings that grow from onion seeds. These are what you transplant into the garden in the spring after starting seeds indoors in winter.
- Scallions are very thin onion bulbs, together with the green leaves that grow above ground. They come from onions that are harvested super early. They are often grown close together in bunches to keep them small, and harvested before they have a chance to grow larger.
- Green onions are similar to scallions, but they are harvested a little later, and so they are little thicker.
- Spring onions are harvested even later than green onions. The bulb is starting to get a little bit round at this point, but it is not a fully-grown onion.
- Onions have been allowed to grow to full size and have a nice, spherical, rounded bulb. The greens of a sprouting onion are leaves that grow up out of the top a mature onion bulb. If you cut these leaves off after harvest, more will appear when the onion sprouts again in storage.
The following table summarizes the differences between onion sprouts, scallions, green onions, spring onions, and mature onions:
| Onion Type | Description |
|---|---|
| Onion Sprouts | Seedlings grown from seed to transplant out into the garden. |
| Scallions | Thin bulbs & green leaves from onions harvested very early. |
| Green Onions | Small bulbs & green leaves, they are thicker than scallions. |
| Spring Onions | Round bulbs & green leaves, a little thicker than green onions. |
| Mature Onions | Large round bulbs, the leaves are yellow & have fallen over. |
Here is what onion sprouts (onion seedlings) look like:
Here is what scallions look like:
Here is what green onions look like:
Here is what spring onions look like:
Here is what mature onions look like:
Is It Safe To Eat Sprouted Onions?
It is safe to eat sprouted onions, as long as you check for:
- Mold – cut off any black spots, or discard the onion if the mold is too widespread.
- Rot – if you start peeling the onion and the flesh is brown and smells of sulfur, then the decomposition process has begun. Cut out the brown parts, or throw out the entire onion if too much of the flesh has turned brown.
- Brown Leaves – if you are cutting up the green leaves of the onion for cooking, throw away any that have turned brown or soft.
Cooking will help to minimize any bacteria that may be present. If in doubt, put an onion in your compost pile and recycle it as a source of nutrients for next year’s garden!
Conclusion
Now you know how to plant onions that have sprouted, and what to expect at harvest. You also know how to make your onions sprout faster if you want to try this experiment for yourself.
If you are looking for heat tolerant onion varieties, you can find some in my article here.
You might also enjoy this article on what to do with extra onions.
I hope you found this article helpful. If so, please share it with someone who can use the information.
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~Jonathon