How Do I Get My Onions to Grow Bigger

Many gardeners enjoy onions, and you can use them in almost any recipe. However, if you find that yours don’t grow well (or at all), you wonder what you did wrong.

There’s no perfect way to grow onions. Most of the tips to make them bigger are things you should already be doing. In fact, you probably aren’t going to see onions as big as your head!

Still, if you’re having trouble getting them to be a decent size, there is hope. Here are eight tips to help you grow bigger and better onions:

Table of Contents

8 Tips for Growing Bigger Onions

1. Plant Early

If you’re having trouble getting large bulbs on your onions, you might be planting them later in the season. The amount of daylight the garden gets dictates when the onions start to form a bulb.

For those in the northern latitudes, summer days are longer than in the south. Therefore, it’s best to plant long-day onions. They start forming bulbs when days are between 14 and 16 hours long and work well for latitudes of 37 to 47 degrees.

Alternatively, short-day onions work well in southern gardens between 25 and 35 degrees. They produce bulbs when there are 10 to 12 hours of sunlight.

This is important because onions grow bulbs when they get enough sunshine. The size and amount of the leaves on the plant help you figure out how large the bulb is in summer. Therefore, if you have puny onion leaves, you see small bulbs.

That’s why you should plant onions early. About four to six weeks before the last frost typically happens is ideal. If you wait until late spring, they don’t have time to grow green leaves and encourage large bulbs.

2. Evaluate Your Options (Seeds, Plants, Sets)

When you’re planning your garden for onion growing, you should understand your options. You can grow from seeds, plants, or sets.

Seeds

Many gardeners get better results when they start with onion seeds in winter. Growing from a seed lets you pick the right onions and sizing. Plus, you can find many varieties than at a local nursery. Typically, you should start the seeds about 10 to 12 weeks before the last frost in your area.

Plants

You can purchase an onion plant if you don’t want to start from seeds. Consider buying them from a nursery or farmer. They grow them from seeds in a greenhouse so that they’re ready to plant.

They’re often better than onion sets but not as good as seeds. The benefit of choosing a good-sized plant is that it competes with weeds and produces larger bulbs. It’s best to get them from a local farmer because they know what varieties grow well in the area.

Onion Sets

An onion set looks like very tiny onion bulbs. Generally, they’re started from the previous year, so this is their second growing season.

While that sounds like a good thing, it can be problematic. For one, onions are biennial, so they flower their second year. This can be pretty, but they don’t produce large bulbs because the energy goes to making the flower.

We don’t recommend using onion sets. However, it’s important to know that they’re available and why you should avoid them.

3. The Right Variety for Your Location

Before you select a variety, there are certain characteristics to understand. Here are the steps involved:

Choose the right type – You need an onion variety appropriate for where you live. It’s easy to look up your latitude and figure out if you need intermediate, short-day, or long-day versions.
Storage or Fresh – How are you planning to use the onions? Do you want to eat them immediately or store them? Many people prefer sweeter onions that don’t store well, but you can find various storage-friendly versions.
Color – There are yellow, white, and red onions. We encourage you to try different varieties and colors to find the ones you like best and grow the biggest.
Select the Variety – Pick a few options and try them out. That’s the best way to learn and experiment.

4. Prepare the Garden Beds Correctly

Instead of tilling each year, consider establishing permanent beds. This layout decreases the preparation time and maintenance required. Plus, when you’ve got the beds all read, it’s easier to get going.

Onions have a shallow root system, so it’s best to use crumbly, loose soil free of large debris. Since the roots stay near the soil’s surface, you only have to deal with the top 7 to 8 inches.

Therefore, don’t dig deep and disturb the soil a lot. However, break up large clods of dirt or clay.

5. Use the Right Spacing

You can plant onions pretty close together with just 6 inches of space on each side. That means it’s easy to fit a lot of onions into smaller gardens.

It’s often tedious because onion plants are small. You can find tools that help you with 6-inch spaced prongs or make your own.

Make sure to plant the onions 1 inch deep. However, if you didn’t trim them in the seed starter, you can cut the top 5 inches off. That way, it doesn’t get dry while the roots establish themselves.

6. Water and Fertilize Correctly

Onions must be watered frequently because they have shallow roots. Keep the top 3 or 4 inches moist around them. Not having enough water stunts growth, but so can having too much!

When you plant the onions, add compost or fertilizer to the soil. We recommend that you do this when you prepare the garden beds. However, you can use liquid fertilizer later in the growing season to give you bigger onions later.

7. Keep Weeds Away

Try keeping your onion bed clean and weed-free because onions don’t like them. If you dislike weeding, consider adding a thick mulch layer to the onions. It keeps moisture in and prevents weed growth.

Though wider spacing makes it much easier to control the weeds, you want to get as many onions as possible. With that, though, you prefer that they grow large. You can up the spacing to 12 inches if needed, but we recommend sticking with 6 inches.

8. Don’t Harvest Until They’re the Right Size

When the onion tops fall over, don’t be alarmed. Many beginner gardeners believe they should harvest them, but that’s not true. If they aren’t the size you want, wait a bit longer.

However, you can’t wait weeks after regular harvest times. Again, you should check your location and find out when traditional harvesting takes place. From there, give it another five to seven days to see if the onions get any bigger.

For example, most northern locations harvest onions in June or July. Start checking them in June, and if they aren’t big enough, wait until July. Just don’t go much more than that, or they could start to rot!

Conclusion

Onions are a great addition to any vegetable garden. If you enjoy cooking, you probably buy them all the time. What’s better than going to your garden, grabbing an onion, and chopping?

Still, you want the onions to be big so that you only need one for a meal. Most gardeners incorrectly believe that they need to use special varieties or do something crazy with the soil.

However, proper nutrients (fertilizer), water, and weeding techniques are all you need. That way, you can protect the ground, grow large onions, and have a beautiful garden!