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Do Onions Grow Underground?

There’s just one straightforward answer we can give to the question do onions grow underground: yes, they absolutely do. If we want to be completely clear we will say that the bulbs grow underground and the leaves grow above ground.

Even if we attempt to grow onions in a hydroponic system, you will discover that it’s not as easy as it is when growing other vegetables just for this exact reason: because onions grow underground. It means that we need a system that comes with a growing medium that has enough profundity and adequate length.

Do Onions Grow Underground? The Entire Process

These are some of the easiest to grow vegetables, you can pretty much do nothing wrong, they require very little knowledge and care.

The anatomy of an onion consists of: roots, bulb (white, yellow, red), leaves, stem, flower (which produces the seeds). The roots and the bulb and the parts growing underground. However, you’ll see that as the bulbs get bigger and bigger, they will start appearing above ground. By the time of the harvest, mostly the roots are left underground.

I mention first the anatomy of this vegetable because I want to let you in on a little thing that I like to do. You can also watch this video for a visual guide.

If you want to grow onions for bulbs but you still want to enjoy eating green onions, you can remove a few leaves from each bulb when the leaves are tender and so delicious. You can enjoy both things and still have a bountiful crop of yellow or red bulbs. It works for all varieties.

Grow onions from sets (small onion bulbs)

grow onions from seeds

You can definitely grow onions from seeds but it’s so much easier to plant tiny onion bulbs, which will speed up the process and make things so much easier.

You can buy the onion bulbs and then plant them directly in the ground. These are also known as sets or transplants. If you want to make a comparison, these sets are just like flower bulbs.

Each set (tiny onion) will grow into a single very big bulb by the end of the growing season.

Sets are planted in the prepared soil, only the tops are left above ground. You don’t have to cover the entire set with soil.

Plant the sets one inch deep and four inches apart in rows that are 12 to 24 inches apart.

The sets will be planted with the roots down and the pointed tip up.

Moreover, if you have planted the tiny bulbs too close to one another, you can do some thinning. You can remove the larger seedlings and eat those removed as scallions.


The soil needs to be fertile, you should definitely use compost. You also need to grow in a well-drained soil, another important reason for adding compost to your garden.

It also needs to be completely clean of weeds.

Once the seedlings start growing, you need to weed by hand because they’re easily damaged. As soon as the onions are a few inches tall, you can add a layer of mulch to keep the weeds away.

Moreover, don’t use a hoe for watering when the seedlings are fragile.

You can grow both onions and potatoes at the same time, they pretty much require the same growing conditions. Potatoes also grow underground, although a single seed potato will produce more potatoes for you to harvest.

Temperature & light

They grow best when they’re not exposed to extremes of cold or heat. Otherwise, there aren’t any other special requirements.

They are planted in cool weather, onions grow underground and are considered a cool weather crop.

These can be among the first vegetables you plant in the spring.

Day-length exposure to the sun is ideal.

However, you might also want to know that there are 2 varieties to choose from: short-day that require 12 hours per day and longer-day that need 15 to 16 hours of sunlight per day, perfect for places with long summer days.

When to Harvest Onions

As they’re nearing harvest, most of the grown bulbs will actually have grown above the soil. They’ll be completely uncovered. Mostly, just the roots and the stem and under the ground by the time harvesting is near.

You will be able to harvest when the tops wilt and they flop over. Flowers can also appear, which means that the onions are completely ready for harvest, as they enter their reproduction cycle.

Remember when we said that the answer to do onions grow underground is yes? Well, when you’re ready for harvest, you’ll have to remove them from the ground and bring them to the surface.

If the roots are strong, it might be a bit difficult. You can insert a fork under the bulb to break the roots’ hold onto the soil.

If the weather permits, let them in the sun to dry before storing them in a cool, dark, frost-free place with good air circulation.

The Wonder of Onions

Onions are some of the oldest vegetables. If you want to read more on their history, you can do so here.

They are often taken for granted but I want us to take this opportunity and truly realize just how special they are as the basis for most of the recipes we make in our kitchens or eat out in restaurants.

Just think about the many ways we consume them: raw, pickled, sautéed, in stews or soups or stir fry, roasted and baked. By the way, is anyone craving onion soup right now or is it just me?

Yellow onions are actually the most common and the variety most frequently used in dishes around the world.

Red onions are a favorite of mine for their sweeter taste, I especially enjoy them roasted or baked. These are also enjoyed raw.

If we take things even further, we can talk about the onion family. Its members also include: garlic, leeks, chives, shallots.

Garlic is just as famous, leeks also grow underground and are absolutely delicious, shallots are a wonder truly explored by the Thai cuisine, and chives, including garlic chives, are actually a herb that it’s very easy to grow even indoors or in a basic hydroponic system.

Chives, scallions, and garlic also grow underground but they don’t grow such large bulbs so, these can even be grown in containers on a balcony or on a small patio.

We can grow garlic plants from garlic cloves. It’s just as easy as growing onions.

Well, we definitely answered the question do onions grow underground and much more than that, I hope you’ll be able to grow a beautiful crop one day.