Skip to Content

13 Common Onion Growing Problems (and How to Solve Them)

Onions are grown for a variety of purposes including cooking and pharmaceuticals. If you try to grow your own onions at home, you may encounter problems. With proper care and attention, you can control many of these onion growing issues. Let's look at some of the most common onion-growing problems and how to solve them.

A collage of common onion growing problem.

Onions are one of the first plants that many gardeners plant in their home vegetable gardens.  They can grow in just about any environment, they naturally repel bugs and other pests, and it’s possible to harvest just about every part of the plant.

There are several problems that onions can have, however.  Fortunately, most issues are fairly easy to correct.  If your onions are not growing correctly or giving you enough to harvest, check to see if you are having any of the problems on this list.

1. Choosing the wrong type of onions.  

Wide field of onions with turquoise sky view.

There are hundreds of varieties of onions, and not every type will produce onion bulbs in every type of climate.  While just about every type of onion will produce green onion shoots, onions that are planted outside of their zone will not produce onion bulbs.  

Unfortunately, if you planted the wrong type of onions, there isn’t a lot you can do to fix the problem.  Depending on what type of onions you have and the season, it may be possible to just wait longer for them to the bulb.  

This can sometimes be the case for onions that were meant for higher temperature climates; waiting until the weather gets warmer means that the onions might bulb later in the season.  Be aware, however, that there is no guarantee of this.

To prevent this problem from happening in the future, be sure to plant the right type of onions for your climate zone.

2. Sets vs. Transplants.

If you aren’t growing your onions from seeds, then you’ll have to use either sets or transplants.  Sets are usually meant to be grown for the green onion shoots, while transplants are meant for growing bulbs.  Unfortunately, a lot of people get them confused because sets tend to already have a small bulb, while transplants are just green shoots with roots.

The problem with sets is that the bulbs rarely tend to get bigger, while transplants will grow a complete bulb once they are planted.  You can harvest green onion shoots from sets, however, so the crop won’t be a total waste.

3. Sets or transplants that are too big.  

Sprouted onion bulbs in egg carton.

When selecting sets or transplants, it’s understandable why a lot of people would pick the largest bulbs of shoots available.  However, larger bulbs that are picked and sold as sets or transplants have their growth cycle interrupted at a critical time, causing the plant to stop growing a bulb after it has been planted.

 To avoid this problem, look for onions sets and transplants that have bulbs and shoots that are no wider than the width of a pencil. In this case, smaller really is better.

If you’re a new gardener, you might want to consider avoiding sets altogether.  It can be difficult to determine the exact right size that you need.  Instead, rely on transplants or start your onions from seed.

4. Growing from kitchen scraps.

Sprouted onion from kitchen scraps.

A lot of gardeners, especially new ones, decide to try growing onions from their kitchen scraps.  We get it; there are plenty of internet videos showing people having a lot of success doing this.  To do this, take a piece of onion, place it in the soil, cover it with about one inch of dirt, and keep it well-watered.  According to most internet videos, the result will be perfectly formed onion bulbs in just a few weeks.

The truth is that results from doing this will vary a lot based on a lot of different factors.  First, be aware that the onion will start to send up green shoots within about 5 to 10 days if it gets enough water and sunlight.  If you like green onions, you can continuously harvest the tops of this onion plant for months or even years if you take care of it.

The bulb, however, will very rarely look like what you buy in a grocery store.  The actual shape you get will depend on your climate, the exact type of onion you planted, the season, soil conditions, water, and sunlight the plant receives.  

Plenty of gardeners have experimented with this and claim that the shape of the bulb can even be influenced by the size and shape of the piece that was originally planted. There may be some merit to this claim, but remember that the bulb you plant will not actually continue to grow back into a spherical onion.  

What actually happens is that the piece of onion will degrade as the green onion top grows, and eventually the tops will form a new root structure that will become the new onion bulb.  That means that planting onions this way will take a long time before onion bulbs are ready for harvest.  Expect to see some really odd shapes from the onion bulbs when you do harvest

Nonetheless, this is a traditional method of growing onions.  For centuries, plenty of families were able to grow new onions using this method, avoiding the need to purchase new seeds every time they planted.  

This method also allowed families to plant and harvest onions throughout the year; every time one was harvested a small piece would be replanted, assuring that within a few months in any given week at least one onion plant would be ready for harvest.  

5. Growing from seed.  

Onions that are grown from seed are just going to take a lot longer to harvest than those that are grown from transplants.  Expect to wait at least three months before having harvestable onion bulbs.  On the positive side, however, you can have green onions available within a few weeks.

6. Planting too deep.  

A gardener planting onion bulbs in garden.

Transplants and sets should be planted so that the green part of the plant is completely out of the soil and the roots and bulb are completely under the soil.  If you plant deeper than this, the green part of the plant will become too moist (since it cannot release moisture during its dark cycle), and the plant will begin to rot.

As the plant grows, you will see the bulb start to rise above the ground.  This is normal, and it will allow you to gauge the size of the bulb.

7. Planting too close together.  

While it may seem as if seeds or starts can be planted within a few inches of each other, it’s a good idea to space out plants with at least eight inches between them.  You can probably get away with six inches of spacing, but anything less makes it difficult for each plant to get enough nutrition out of the surrounding soil.

8. Under fertilizing or overfertilizing.  

A bag of fertilizer in onion garden.

While onions are a plant that generally requires relatively little fertilizer, if they are planted in poor soil you’ll start to notice problems.  Specifically, if the onion greens are too thin or stunted and the onion bulbs aren’t developing right, you may have a problem with the quality of your soil.

Ideally, plant onions in good soil with a thick layer of compost, or mix the compost into the soil.  Avoid sandy soil and soil with extremely high pH.  Onions tend not to take a lot of nutrients from the soil, so many gardeners are able to get several harvests before they need to mix in more fertilizer.  

If you have poor soil, add small amounts of fertilizer slowly into the soil (spread out applications by at least a week).    Because bulbs grow underground, they can be prone to fertilizer burn. One of the nice things about onions is that they can be grown in a range of soils.

In fact, this is part of what made onions so appealing to grow for even the poorest families.  Onions have been grown in undernourished soil for centuries, and in fact, they have been one of the last crops that many families were able to harvest after weather conditions wiped out many other plants.

9. Overwatering.  

Onions need water, but soil that is too moist can cause the bulbs to rot.  Keep the soil around the onions slightly moist, but do not allow standing water to pool around the plants.

10. Underwatering.

Do not neglect the plants either.  If the soil does not get enough water, the top part of the plant will turn brown.  

11. Too much shade.  

Onion plants covered with plastic.

Onions are capable of growing in a lot of different types of light, but they still need a few hours a day of direct sunlight.  This is so that the green tops are capable of photosynthesizing enough light to feed the rest of the plant.  

Without this sunlight, the entire plant will shrivel, turn yellow, then brown, and eventually die.  Onions that are grown in too much shade can also be susceptible to mold and mushroom growth.

Be aware that it’s really hard to expose onions to too much sunlight.  In fact, we didn’t even bother to include it as a possible problem on this list.  In extremely hot climates it is possible to sunburn the leaves of onions, but usually only occurs in temperatures over 110 degrees.

12. Too many weeds.  

Weeds can crowd out your onions, even if you don’t see a lot of them above the ground.  Weeds that have complex root structures can essentially strangle a plant, making it impossible for onion bulbs to have enough space to grow.  Be sure to pull any surrounding weeds out and remove the entirety of the roots when you do.

13. Bolting. 

A flowering onion plants in garden.

Like all plants, onions will eventually form flowers which will make seeds.  In onions, this usually occurs when the temperature gets too hot or the plant gets too old.  Once the plant bolts, or forms flowers, it will no longer produce onion bulbs; all of the plant’s energy will be focused on making seeds.  

Because bolting will usually happen at the end of the plant’s natural life cycle, there isn’t much you can do to stop the process.  Save the seeds from the flowers, and start a new crop.