How do you grow onions in aquaponics?

Growing onions in aquaponics require a combination of many factors, such as the type of onion you will raise, how you will purchase your onions, what aquaponics setup you will adopt, and other essential growth requirements. This post will help you understand how onions thrive in a recirculating aquaculture system such as aquaponics.

Why grow onions in aquaponics?

Onions are easy to manage.

These crops are an excellent introductory veggie for beginners in the garden since they are easy to grow and require little care. Onions are common options for city gardening because you can grow them in small spaces such as pots or small containers.

Onions are classified as specialty crops.

Plants that are actively grown are known as specialty crops. These crops have high market demand because many people use them for medicinal or culinary purposes. Onions are almost included in many dishes, served in our homes or restaurants.

Onions require an adequate amount of water.

Another good reason for including onions in your grow beds is they have high water demand. This is why a good aquaponics technique for onions is the deep water culture because its roots are completely immersed in nutrient-rich waters.

Onions are nutritious crops.

Onions are high in plant compounds, including flavonoids, which have anti-inflammatory and antioxidant properties. When consumed in adequate amounts and regularly, these substances may help protect against chronic diseases, including cancer and diabetes.

Furthermore, a specific study about peri- and postmenopausal women proves that frequent onion eating can reduce the incidence of hip fracture.

Onions can repel certain plant pests.

One known benefit of onions is their ability to repel destructive pests. The smell of onions also repulses insects such as aphids and mites. Onions can be mixed with water and poured around the base of plants to keep bugs at bay.

What are the different varieties of onions?

Onion varieties could be based on their required sunlight and the region where they are grown. Here three groups are known: short-day, intermediate-day, and long-day onions.

Short-day onions: When the daylight length exceeds 10 to 12 hours, the bulbing process begins in the short-day onion cultivars. These onions are suited to grow in latitudes of 25 to 35°. They mature in around 110 days in warm climates, while they mature in about 75 days in cold temperatures.

Here are the best-known onions for this variety:

  1. Texas Super Sweet
  2. Yellow Garnex
  3. White Garnex
  4. Texas Sweet White
  5. Sweet Red

Intermediate-day onions: Since they require 12 to 14 hours of sunshine before commencing the bulbing process, intermediate-day onion types are the most flexible. If your region is found at latitudes of 32 to 42°, you can grow these onions.

Below is a shortlist of intermediate-day onions:

  1. White Super Star
  2. Sweet Yellow Spanish
  3. Sweet Red Onions

Long-day onions: The last variety of onions requires 14 to 16 hours of sunlight. They are ideal for growing in regions along the northern latitudes, 37 to 47°.

Here are known long-day onions:

  1. Walla Walla Sweet
  2. White Sweet Spanish
  3. Yellow Sweet Spanish

Which variety is best for aquaponics?

Because onions rely so much on water, every variety I mentioned above would be ideal for aquaponics. Nevertheless, it would be best to determine which onion type grows well in your climate and has high market demand.

Now, experienced growers would recommend growing short-day onions. Practically, these cultivars would only need 10 to 12 hours of lighting to transition from their vegetative state to bulbing. So, you will save much time in growing short-day onions compared with the others.

What aquaponics method is best for growing aquaponics?

The three general aquaponic setups work well in cultivating onions.

  1. Media bed: This approach is convenient for home growers just starting in aquaponics. If you decide to grow onions via this technique, the recommended media would be clay pebbles or gravel.
  2. Nutrient film technique: The roots of the onions are allowed to dangle in a PVC pipe with holes in this design. Before being pumped back into the tank, the water is sucked into the pipe and run over the roots, supplying much-needed nutrients. This method is appropriate for growing crops vertically, horizontally, up walls, or even hung from ceilings. NFT is also flexible enough to allow crops to be grown vertically, horizontally, up walls, or even hung from ceilings.
  3. Deep water culture: Due to the specific growing requirements of onions, some growers use the deep water culture or DWC. Its process is straightforward, but it yields an abundant harvest of crops. This fact is one good reason why DWC is preferred by those who do aquaponics for commercial purposes.

What factors to consider to grow onions in aquaponics?

Purchasing onions

There are three ways to purchase onions to fill your grow beds. You can buy onions by transplants, sets, or seeds.

  1. Transplants: These are seedlings that have been started during the current growing season and are sold in bunches by nurseries. They produce good bulbs in a short time (65 days or fewer). One known downside is that they are susceptible to illnesses. You can also choose limited cultivars among transplants.
  2. Sets: These types are immature bulbs from the previous year. Sets are known to have the least cultivar selection. You would appreciate sets because they are the simplest to grow, the earliest to harvest, and the least disease-prone. On the other hand, onions grown from sets are more prone to bolting.
  3. Seedling: Growing onions from seedlings gives you a wide variety of cultivars to choose from. If they grow from seeds, one challenge growers must take is that the crop would require four months to mature. Onion seedlings must be started indoors by gardeners in colder climates.


  1. Water: To stimulate the bulb to sprout, you should secure a water temperature between 55 and 75 degrees Fahrenheit (13 to 24 degrees Celsius).
  2. Air: The air temperature in your garden should be the same as or slightly higher than the water temperature. This situation will stimulate the sprouts to travel in the direction of the Sun. Onions can withstand a wide range of temperatures and are frost-resistant. Cool temperatures of 55° to 75°F (13°C to 24°C) accommodate leaf, root, and bulb development. Temperatures of 68° to 77°F (20° to 25°C) facilitate onion leaf growth.

pH range

Onions are known to absorb large quantities of water. Therefore, your water quality, such as the pH, will directly impact the onion's flavor. The optimal pH range for onions is between 6 and 7. This range keeps the water neutral and allows the onion to develop its distinct cultivar flavor. Moreover, most fish and other crops thrive in this pH range, so your onions can be a good companion plant to other aquaponics greens.


As discussed above, this factor relates to the variety of onions you choose to take care of. Regardless of the cultivar you are growing, onions demand full sunlight to achieve desirable growth. Hence, you should ensure that your growing bed has access to abundant light coming from the Sun. Artificial lighting may also work if sunlight exposure is a challenge in your region.


If you aim to harvest large onion bulbs, the recommended spacing would be four to five inches apart. Some even adopt more expansive space between the plants: 12 to 15 inches apart.

Fish companion

When it comes to fish companions for your onion growth, you will have to rear those that produce many excrements. The reason for this is that onions have high nutrient demand. Because of this, you can have tilapia, goldfish, and koi.

How long does it take to grow onions in aquaponics?

The time it takes to harvest your onion veggies depends on how you purchase them.

If you started from seedlings, the average growing time would be 90 days or even up to five months. For onions grown using transplants, the maturity of the bulbs could take 60 to 80 days. Sets grow the quickest. You can expect a harvest from sets within two months at the very least.


Onions are a great addition to any aquaponics garden. This crop type does not require much attention if you meet its recommended growing parameters. By applying the information, this article provides, you are ensured to harvest delicious onions, which you can use to improve the taste of your home dishes.

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