How To Grow Hydroponic Onions (Complete Guide)

Hydroponics is fast becoming a popular way to grow various plants for aesthetic reasons and food. Onions, like lettuce, tomatoes, and spinach, can be developed using hydroponic farming methods and in the same fashion as hydroponic herbs like basil, oregano, thyme, and cilantro. However, cultivating hydroponic onions is a straightforward process that you can achieve by following a few simple steps.

Here’s how to grow hydroponic onions:

  1. Choose an onion species that is appropriate for your needs.
  2. Start your onion seeds.
  3. Prepare the hydroponics system.
  4. Assess the hydroponics system’s conditions.
  5. Transplant your onion seedlings.
  6. Maintain your hydroponic onions.
  7. Harvest the onions.

Onions are the easiest hydroponic vegetables you can grow using small-scale or large-scale farming techniques. You can maximize the onions’ growth as long you maintain the growing conditions of the system. Read on to learn how to grow hydroponic onions from bulbs and learn the essentials of hydroponic onion farming.

1. Choose an Onion Species That Is Appropriate for Your Needs

Hydroponic onions may be grown from seeds the same way as hydroponic herbs are cultivated. The procedure is simple enough for beginners and hydroponics specialists to complete. 

However, from the beginning to the end of the process, you must carefully monitor, regulate, and maintain the hydroponic system’s environmental conditions.

The common onion, also referred to as the bulb onion, is one of the world’s most extensively grown crops. The vegetable, which is related to leek, garlic, chive, and scallion, is used in salads, soups, sauces, and spices.

Many species of onions may be used in hydroponics, but the green onion is the most preferred kind that is usually cultivated. They are the easiest vegetables to grow since they are so small. These plants, also known as scallions, are often picked before the bulb emerges from the stem.

However, the bulbs of Green onions are often significantly smaller than those of other species of onions. Green onions are naturally adapted to hydroponic vegetable cultivation, and hydroponic growers prefer them for their gentler, more delicate flavor. 

Furthermore, you can consume the entire plant rather than simply the bulb.

Onion Species That Are Good for Hydroponics

Onion species are classified into three distinct groups based on the period it takes to mature from seeds, which include the short-day onions, intermediate onions, and long-day onions. However, you should pick a species you can adequately maintain with the resources at hand. 

Although green onions are at the top, other onions are suitable for hydroponics. The following species of onions are suitable for hydroponics:

  • Texas super sweet onions: The Texas Super Sweet Onion is a big, yellow tasty onion that matures in 105 to 110 days and has a somewhat flattened look. It is one of the most popular short-day type onions, as it has a slightly later maturity date than other species.
  • Yellow granex onions: This Granex-type onion, also called Georgia Sweet Onion, is a mix between a round Grano and a flatter Bermuda onion and is the sweetest of the sweet onions. It is a huge, yellow, squashed-looking, globe-shaped onion with a crisp texture and takes 110 to 160 days to mature.
  • White granex onions: The plant grows thick, flat, and mild-flavored bulbs and is often known as Texas Sweet Onions. White granex onions are a white variant of the yellow granex onion and are usually disease-resistant.
  • Texas sweet white onions: This onion may be found in several restaurants and adds flavor to a range of sautéed and grilled meals. Its thick, flat bulbs mature after 100 days, and its flesh is firm, dry, and mellow.
  • Sweet red onions: Sweet red onions are the product of more than two decades of breeding and are a flat type with a distinctive form. Sweet reds, native to Italy, have a moderate flavor that is neither overbearing nor harsh, making them ideal for a range of dishes that call for a mild yet sweet taste.
  • White Bermuda onions: They produce small, pale, mild-tasting, flat bulbs and are sometimes called Cocktail Onions or Crystal Wax Onions. White Bermuda onions mature in 85 to 95 days and can be used in sauces, soups, and food preservation.

The best Onion kinds to grow in a hydroponic system are those of the short-day group like the species above. Using a hydroponics system to produce onions will almost certainly require growing lights, air pumps, and heaters. 

Appliances like these tend to use a lot of power, which may be pretty expensive in the long term.

For example, short-day onions require less light to transition from vegetative to bulbing. So, instead of planting long-day onions and needing to keep them in the sunshine for 15 hours a day, you can grow short-day types that need 10 to 12 hours of light every day.

The capacity to resist cold is another advantage of cultivating a short-day variety under hydroponics. Short-day onion cultivars are a great way to save money while still producing enormous onions.

However, you should ensure that the species of hydroponic onions you cultivate have a reasonable growth rate and yield, high disease resistance, and good flavor.

2. Start Your Onion Seeds

Like those grown in typical farms, hydroponic onion seeds require enough water, dissolved oxygen, and the right temperature to thrive. Water and oxygen will be absorbed through the seed coat when it is exposed to ideal circumstances, and the seed can germinate into a plant.

The following are the two ways you can get your hydroponic onion seeds started:

  • Starter plugs
  • Direct sowing

The method you use to start your onion seeds is primarily dependent on the scale of your system, as well as the species of onion you decide to grow. However, the hydroponic technique you plan to grow your onions with is also a significant factor in determining what seed starting method will work for you.

Starter Plugs

Growing your hydroponic onion seedlings in soil or a different hydroponic grow system before putting them in your hydroponics farm is a terrific way to get them started. Once the seeds have reached the required size, make a tiny hole in your hydroponic growth medium and delicately place the seedling inside. 

After that, use your grow material to shut the plug properly.

Your onion seedling might need some support at first, so you can use stakes or ropes to keep the seedling from tumbling over. Using supports will also help keep the plant in the system until the roots emerge through the plug.

While various starting plugs are available, the most common are compacted peat, clay, and paper towels since they are economical, clean, and easy to get.

To see a visual of how to do this, check out this YouTube video. 

Direct Sowing

Direct sowing is the process of planting onion seeds directly into your system. 

Direct seeding is employed in hydroponic systems previously modified for plant growth. This method works well in a media-based hydroponic system, where the media, such as pebbles, Rockwool, or sand, may aid seed development.

Ensure you spread the onion seeds equally over the grow media, pressing them down into the top dry layer and allowing them to sprout naturally. 

However, because some seeds germinate better than others when planted directly, it is a good idea to disperse many seeds when sowing. The primary benefit of direct sowing is that it eliminates the need to relocate your seedlings to a grow bed, lowering the risk of root damage.

Furthermore, because this method needs a lot of sowing, scattered seeds need to be tended as they bud, plucking out excess to minimize crowding.

Overcrowded plants will be malnourished. Early malnutrition can cause a plant to become weedy and sickly for the remainder of its life, so be sure to remove any extra or wilting plants to create room for your onion shoots.

Most hydroponic farmers recommend that you use direct sowing for onion seeds to ensure the plant is well cared for from the start of the cultivation process.

3. Prepare the Hydroponics System

Starting a successful onion hydroponics system demands careful planning of all areas and components of your farm, including the best place to site it. 

As a result, getting your garden off to a strong start entails more than just spreading onion seeds. The hydroponics system can consist of a tank, grow bed, air pump, water pump, tubes, and containers.

You can prepare your hydroponic system for onion cultivation by following these steps:

  1. Choose a suitable container for your hydroponic onions. The container can be a tank, a bucket, or even a large jug.
  2. Fill the container with nutrient-containing water. Fill a jar nearly to the full with water, then add a vegetable fertilizer explicitly made for onions, making sure to follow the guidelines on the packaging.
  3. Add an air pump to your farm. Like most life forms on earth, plants need oxygen to grow and flourish. An air pump is necessary to aerate the system and improve dissolved oxygen in your hydroponics farm.
  4. Place the system under the light. Set the container in a location that gets plenty of sunshine throughout the day. If you do not have access to a space with plenty of light, use a grow light to keep the system running alive.

Before you even think of adding onion seeds to the system, be sure to set the proper groundwork. 

To make sure your onion stays healthy, you need to use the correct technique for hydroponic onion growing, and your system must contain adequate vital minerals. Likewise, the system’s ambient conditions must be ideal, including the pH, temperature, and dissolved oxygen levels.

4. Assess the Hydroponics System’s Conditions

Once you’ve prepared your hydroponics system and created proper conditions on the farm, you may finally concentrate on transplanting your onion seeds. While the planting method is vital, ensuring that the system has favorable conditions for the hydroponic onion to flourish is critical.

The next section of this article, which describes how to manage your hydroponic onion system, also examines the proper levels at which your onion system may grow.

Conditions To Maintain Hydroponic Onions

Maintaining a hydroponics system is an integral part of growing hydroponic onions. To guarantee the system’s environment is at ideal levels, you will need to examine and adjust vital conditions in the system’s water as often as feasible. Your onion’s hydroponics system must always be suited for the plant’s survival if it is to flourish.

The following conditions should be measured and controlled to keep hydroponic onions healthy:

  • pH: The pH level of the system should be maintained between 6.0 and 6.7 for your hydroponic onion to flourish.
  • Temperature: The farm temperature should be between 55 and 75°F (13 to 24°C).
  • Light: Hydroponic onions need 10 to 16 hours of sunlight each day to thrive.
  • Air: Adequate air supply is essential to protect your onions from bacteria and mildew. Exhaust fans are one of the various options for providing appropriate air circulation.
  • Dissolved oxygen: Aeration is the process of providing adequate oxygen to roots, which is essential for healthy development. It aids in the effective absorption of nutrients by the roots.

5. Transplant Your Onion Seedlings

Transplanting is the process of introducing germinated plants from another area into your hydroponic system. This technique is simple and can be finished in only a few steps. It would be best if you only transplanted onions that start from starter plugs as seeds directly sown do not need to be transplanted.

Here are the steps you need to take to transplant your hydroponic onions:

  1. Make room for the seedling you want to move. This stage comprises making enough area for the seedling to increase the onions’ chances of survival. Make sure the seedling has adequate room to develop without competing for nutrients.
  2. Thoroughly rinse the seedling. This step is optional, but it is a great way to accelerate the growth of your onion seedlings. Rinsing your plant in a water and fertilizer mix can significantly increase root and overall plant development.
  3. Place the seedling in the system’s growing medium. Once you’ve finished the previous processes, place the seedling in the location you have established for it, being careful not to damage its roots throughout the transplanting process. Cover the roots with the medium surrounding them after you are satisfied with the crop site.

The transplanting process can cause some damage to the roots or bulbs of onions, but you can use rooting compounds to aid regrowth. 

It is a good idea to avoid using fertilizers for your onions before they are transplanted as they may damage the seedlings.

Here’s a YouTube video that shows how to transplant onion seedlings:

Techniques Used In Growing Hydroponic Onions

Deep Water Culture (DWC)

In the deep water cultivation method, commonly known as the raft or float method, onion roots are suspended in nutrient-rich, aerated water using floating rafts with holes. This technology is extensively employed in large-scale hydroponics systems that cover large spaces.

Plants are cultivated in rock wool before being transplanted into pots that fit holes drilled in a floating polystyrene raft. In deep water culture hydroponics, polystyrene rafts are often used because the material insulates the water and prevents algae formation by blocking light.

The water is aerated with an air pump to guarantee that the roots of the plants have adequate oxygen to absorb the nutrients.

The deep water culture system is also the most reliable hydroponic farming method for various plants since it consumes more water and reduces the risk of water shortages. Furthermore, a raft may support plants with a more extensive root zone than a nutrient film system (NFT).

Other advantages include the simplicity with which you may harvest onion bulbs and the reusability of the rafts. Commercial organizations extensively use this method because of the vast grow beds and added filtering. 

Furthermore, the technology is simple to scale and perfect for large-scale, high-yield operations.

Kratky Method

The Kratky method combines approaches for cultivating and preserving crops. In this approach, a half-grown onion is immersed in water, and the onion becomes larger and leafier over time. Therefore, using the Kratky method to grow hydroponic onions means that you start with preparing your hydroponics system.

Nutrient Film Technique (NFT)

You may use the nutrient film method to grow onions in long canals made of PVC pipes (NFT). 

The plant’s roots hang from the holes and into the channels, absorbing nourishment from the water below. A thin layer of water flows down the canal at all times, carrying nutrients and oxygen.

Onions, basil, leafy greens, and other plants with a bit of root mass that do not need support to develop can thrive using this strategy. Larger fruiting plants may be too heavy for the canal, and some onions that grow large bulbs may obstruct the system with their roots.

Nutrient films may be used vertically or horizontally and are ideal for small spaces. The canal used in the nutrition film technique is generally PVC because of its durability.

Wick Systems

One of the oldest ways for cultivating hydroponic vegetables is the wick system which employs a passive hydroponic technique and requires no electricity to use. 

However, it is not a scalable method of cultivating hydroponic onions.

The nutrients are transferred to the roots of plants via a wick, such as a length of rope. Nevertheless, the Wick system is an excellent strategy for cultivating lesser onion types efficiently.

Media-Based Hydroponics Technique

Hydroponic onions can also be grown in containers with a growth medium that feeds their roots in media-based hydroponics systems. 

Water is regularly poured into the grow beds from a tank or another source to flood the beds and offer nutrients to the plants. If you do not want to utilize a pump, you can manually add water to the system.

The medium supports the plants while also acting as a biological and mechanical filter for the water used in hydroponics. You may use this method to grow deep-rooted plants like vegetables, fruits, flowering plants, and root crops.

The plants are usually arranged vertically above the tank, and beginners and seasoned hydroponic onion gardeners will benefit from the media bed approach as it saves a lot of space.

The system is low-cost, easy to build, and does not require further filtration. It is ideal for small-scale farms.

6. Maintain Your Hydroponic Onions

You’ll still need to care for your hydroponic onions once they have been transplanted. You will need to be careful with them from when they are planted until you are ready to harvest the onions. 

To guarantee that your hydroponic onion thrives, you must carefully measure and regulate all of the parameters in your farm. Light, pH, nutrition levels, and dissolved oxygen levels are all things to consider.

7. Harvest the Onions

You can pick Green onion stalks about three weeks after planting, but bulb onions take 80 to 140 days to mature. Hydroponic onions are harvested the same way as onions are grown in a regular garden. 

The best time to pick hydroponic onions is early in the morning.

The harvested onions are ready for use as soon as you pick them up. If you notice flower stalks coming from the onions, it means they have reached the end of their growth cycle and are ready to be harvested. Yellow and tipped-over foliage is another sign that your onions have developed.

Allow your onions to dry after harvesting. 

This process is called curing, which can be done by laying the plants out on a level surface with sufficient air circulation and cold temperatures. If stored in a box or an old onion bag away from direct sunshine, they should survive many months.

Growing Hydroponic Onions From Bulbs

You can grow onions from bulbs in the same fashion as from seeds. However, you must swap out the second step to add your onion bulbs to the system. You must ensure to set up the hydroponics system as highlighted in the preceding section.

If you wish to start with the onion bulbs, separate the bulbs in an external medium, such as growing from seeds using a starter plug. When the tiny sprouts appear, carefully transplant them to the hydroponic setup for more efficient and controlled development.

Placing the bulbs immediately into the growing medium will not yield satisfactory results since the bulbs will be unable to acclimatize. Ensure the level of essential minerals is high enough before placing the bulb into the system, as the bulb may not grow if the amount of nutrients is low.


You can grow onions from seeds or bulbs by following simple steps. Several onion species are suitable for hydroponic growing, but the green onion is the most preferred by many hydroponic farmers. 

However, you must ensure to monitor and control the conditions of the hydroponic system to make sure your onion flourishes.

Alexander Picot

Alexander Picot is the principal creator of, a website dedicated to gardening tips. Inspired by his mother’s love of gardening, Alex has a passion for taking care of plants and turning backyards into feel-good places and loves to share his experience with the rest of the world.

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