Can You Plant Onions That Have Sprouted? (4 Steps to Take)


Do you have sprouted onions in your cupboard or on the kitchen counter?  If so, you are probably wondering whether you can plant them (and if so, how to do it and what to expect).

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 first & plant the sections apart to give them room to grow. You can also harvest seeds from the flowers that grow from the stalk on an onion in its 2nd year.

Of course, when planting a sprouted onion, you won’t get a large and spherical globe-like onion that you get when planting from seed.  However, you can turn one large sprouted onion into several smaller ones over the course of a growing season.

You can also allow the sprouted onion to form a stalk, flower, and seeds after you plant it.

In this article, we’ll explain how to plant a sprouted onion. We’ll also talk about why onions sprout, and we’ll show how their life cycle works.

Let’s get started.

Can You Plant Onions That Have Sprouted?

You can plant onions that have sprouted to get more onions.  If you plant a sprouted onion, you can get one or more smaller onions to grow.

Once the green leaves on top of the onion are large enough, you can also harvest those.  You can chop up these green leaves and use them for cooking to give a dish some nice onion flavor.

sprouted onion
You can plant a sprouted onion, but it might be better to separate it into parts before planting. You can also chop up the green leaves to use for cooking.

However, planting the entire onion might not work out so well. First of all, there are different types of onions, which grow 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 may not grow to their full potential.

You can learn more about short-day, intermediate-day, and day-neutral onions from the University of Minnesota Extension.

Also, if the onion is old enough, it might begin to rot inside. If you plant the rotten part of an onion, the rest of the flesh may rot if the soil is too wet.

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.

onion skin
Remove the skin from your sprouted onion first.

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.

white onion roots
White roots like this will start to grow as the green leaves form on top of a sprouted onion.

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 may be pretty long.  If the onion has just started to sprout, the roots will be small and weak.

sprouted onion with white roots
An onion that has sprouted green leaves on top may start to grow new white roots on the bottom. After separating into sections, you can encourage these white roots to grow by soaking them in water.

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 the 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 will add some nutrients for the plant, along with organic material for 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.

onion leaves growing
When planting sprouted onions, leave a few inches between them to allow space for growth and to prevent competition.

This will allow room for them to grow and “bulb up”.  It will also prevent competition between nearby plants.

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 I wrote.

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, an 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.

8 onion flower and seeds
After an onion plant sends up a tall stalk, a white flower will appear at the tip of the stalk. Black seeds will appear later, which you can harvest.

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).

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.

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 white flowers and black 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.

onion life cycle
The life cycle of an onion: seed to seedling to plant to bulb to stalk to flower and back to seed!

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.

onion flower and seeds
An onion plant will eventually send up stalks that produce flowers and seeds, to try to make a new generation of onions.

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.

According to the Ohio State University Extension, the temperature should be 32 to 40 degrees Fahrenheit (0 to 4 degrees Celsius) for best storage.

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.

tomatoes and potatoes
Tomatoes and potatoes both 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.
ScallionsThin 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.
This table summarizes the different types
of onions, from sprouts to mature onions.

Here is what onion sprouts (onion seedlings) look like:

onion seedling sprouts
Onion seedlings emerging from the soil in spring.

Here is what scallions look like:

scallions
Scallions are harvested when the onions are very young. They are often grown together in bunches.

Here is what green onions look like:

green onions
Green onions look like scallions, but are a little bigger because they are harvested a little later.

Here is what spring onions look like:

spring onions
Spring onions are even older than green onions, and as a result, the bulbs at the bottom have started to round out.

Here is what mature onions look like:

onion plants
Mature onions are full-size globes. The green leaves will start to turn yellow and fall over when an onion bulb is mature.

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.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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