Whether you call them spring onions, scallions, or green onions, they are the go-to vegetable for chefs across the globe. Cooks in Mexico, Catalan, Japan, Nepal, China, Vietnam, India, Ireland, and the Philippines use them for various recipes. But we’re here to learn how to grow green onions hydroponically.

Green onions are a part of the Allium (Latin for garlic) genus. There are hundreds of species in the family which include:

To name just a few of the domesticated crops. Most Allium species naturally originated in the Northern Hemisphere, with a few exceptions that grow in Chile, Brazil, and tropical Africa (South Africa).

These plants all produce a chemical compound that is derived from cysteine sulfoxides, which gives them that onion/garlic taste. Also, the bulb structure is either solitary or clustered; for green onions, it is a small single bulb.

Now that we’ve gone through the history of green onions, it’s time to talk about the ideal growing conditions for them in hydroponics.

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Related: Best Hydroponic Plants - Top Herbs, Vegetables, and Fruits To Grow Hydroponically

Optimum Growing Conditions for Hydroponic Green Onions

Green onions are arguably the easiest to produce in a system for hydroponically cultivating a crop.

While you can germinate the seeds in water, most will suggest that you sprout the seeds and grow them first in soil. When germinating the seeds, ensure they are kept moist for around seven to 14 days until a sprout emerges.

If you are planning to grow them outside, wait for spring or until the last of the winter frost has disappeared. Their bulbs don’t like frigid conditions. But they'll most likely be indoors if you’re growing them hydroponically.

You will want to wait two to four weeks before separating the seedlings. And with green onions, you will want to plant them at least two inches apart to allow the bulb to grow. The small bulb size allows you to pot them in smaller net pots, as it only requires around an inch of growing medium.

If you have germinated the seeds in the soil, you can circumnavigate the issue of soil-born diseases by using a sterile growth medium. These include coco peat, coco coir, vermiculite, and LECA (lightweight expanded clay aggregate).

Be aware that a harder growing medium will hamper the bulb growing, but as the bulb is relatively small, this shouldn’t be an issue.

Green onions will need at least six hours (and as much as nine hours) of full sun. The temperature range can vary between 60°F - 75°F. If you plan to grow them through winter, you can use a heating pad or cover the roots with a thermal wrap.

Green onions are sensitive to drought and like having a moist growing medium. The nutrient solution in the system needs to be 6 to 6.5 pH, with an electrical connectivity EC of around 1.8 to 2.

Whatever you want the outcome to be with your crop, whether for the whole plant or used as microgreens, will decide how you prune them. If you are thinning off the tops of densely sown seeds, you’re producing microgreens, and generally, with the whole plant, you are hard pruning.

As a leafy green plant, you will want to fertilize the plants with a nitrogen-rich mixture. Liquid fertilizers with fish or seaweed additives will work well, especially if it is a liquid one.

You can use slower releasing nutrients, but with your N-P-K ratio, you want it to be a nitrogen-rich mixture.

Be aware that green onions can be exposed to too much moisture, which will develop into root rot. And if they are too hot, they will bolt and flower. Pests for green onions are thrips and aphids, which you can treat with neem oil.

Using organic methods to control pests is always better for hydroponic crops as chemicals can drain into the water used by all the plants.

You should be ready to harvest your hydroponic green onions within 80-95 days of sowing the seeds.

Height-wise, the green hollow leaves top out at around six to eight inches tall. And you can gently harvest them by pulling them out.

Now that we highlighted the best conditions let’s talk about the best hydroponic setup for green onions.

Best Hydroponic System For Green Onions

Green onions are easily cultivated in hydroponics. You can even propagate used green onions by placing a bulb with roots in water and allow them to grow more roots.

Green onions are easy enough to grow in water, allowing them to thrive in most hydroponic units. With a need for moist growing medium and small bulb sizes, you can tailor your setup for your personal needs.

Most experts will resort to using deep water culture systems (DWC), ebb-and-flow systems, and floating raft methods. You can even use a simple Kratky system.

Check out our guide for choosing the best hydroponic system

Your crop size and what you want to use the crop for will determine the method you select. Our top choice for green onions is either a DWC or ebb-and-flow system.

With the DWC system, you will grow larger green onions and most people who use this method want to harvest the whole plant. While with ebb-and-flow, you will be more inclined to harvest the baby green onions for microgreens.

Regarding lighting, you will want to invest in a full-spectrum hydroponic LED light due to the hours of sun the plant requires. Also, installing a temperature and humidity gauge will prevent pests and molds from taking hold in the growing area.

As mentioned, high temperatures will encourage the plant to bolt, and high humidity will invite fungal diseases from taking hold. To treat these issues, installing a simple clip-on fan will do.

And you can also combat fungal issues with sprays of bicarbonate-based solutions. Or with potassium bicarbonate or soluble silica.

Now, for the simple step-by-step growing process.

Step-by-step Of Growing Hydroponic Green Onions

When germinating your seeds for your hydroponic system, you will want to use a sterile growing medium. As we mentioned, this will reduce the risk of transferring soil diseases.

Pinch a small hole into the growing medium around ⅓ inch deep, and sprinkle the growing medium on top. Green onions do prefer soft and fluffy growing medium.

If you are planting in one seedling tray, ensure the seeds are at least ¼ inch apart.

After the seeds have sprouted, remove the seedlings from the growing medium and plant them into the hydroponic net pots. If you are using a different grow medium, wash off the roots before transplanting.

You will want to allow the seedling's roots to be moist but not completely wet. The roots will eventually seek out the water source.

As green onions can be harvested for their leaves, you can top them when they reach about six to eight inches tall.

And as a perennial plant, you can harvest a single green onion for many years before they die away.

When you harvest them, place the greens into a partially filled jar of water in your fridge to lengthen the storage time. Otherwise, they will wilt.

So now you know how to grow hydroponic green onions.

Get Started With Hydroponics By Growing Green Onions

As crops go, green onions are great for hydroponic gardeners. They are easy and love being grown in a well-maintained system.

This is the crop to select if you’ve been worried about venturing into hydroponics. But once you’ve perfected it, you will have a continuous supply of fresh green onions.