How To Grow Hydroponic Onions

If you're looking for a cleaner, more efficient way to cultivate one of your favorite veggies, consider growing hydroponic onions.

It sounds tough, but with the right skills, equipment, and know-how, it can actually be really simple and straightforward.

Those interested in learning how to grow onions hydroponically have come to the right place.

Our complete guide is going to explain just why so many gardeners are switching to this style of growing. We'll cover the benefits of growing onions hydroponically.

We'll also explain what exactly you need to get started, along with how to actually grow these. We've got a lot to cover, so let's jump in!

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How To Grow Hydroponic Onions


If you're looking for a cleaner, more efficient way to cultivate one of your favorite veggies, consider growing hydroponic onions.

It sounds tough, but with the right skills, equipment, and know-how, it can actually be really simple and straightforward.

Those interested in learning how to grow onions hydroponically have come to the right place.

Our complete guide is going to explain just why so many gardeners are switching to this style of growing. We'll cover the benefits of growing onions hydroponically.

We'll also explain what exactly you need to get started, along with how to actually grow these. We've got a lot to cover, so let's jump in!

Can You Grow Hydroponic Onions?

Growing your own vegetables is incredibly rewarding. Not only will it provide you with the vegetables you love to eat, but it can also help you save money and improve your overall health.

Hydroponics is a method of gardening that does not require the use of soil. Instead, you'll rely on nutrient water or moist air to cultivate your plants.

Can You Grow Hydroponic Onions?

The ideal method of gardening for people who live in urban environments or are otherwise limited in space, hydroponics is a gardener’s dream.

You might be wondering whether you can grow onions hydroponically - and we’re here to tell you that not only can it be done, but it’s relatively easy.

In fact, onions are some of the easiest plants to grow in a hydroponic system.

How Long Does It Take To Grow Onions Hydroponically?

Depending on what kind of onions you are growing and whether you are planning on harvesting just the tops or the bulbs, it takes around three to ninety days to produce a crop of hydroponic onions.

Green onions, the fastest-maturing kind of onions you can grow in a hydroponic system, take just 21 to 30 days to reach maturity.

For any kind of onions, seeds usually germinate in about 6 to 10 days.

What Do You Need To Grow Hydroponic Onions?

There are several materials you will need to get started with growing hydroponic onions, including the onion sets themselves, water, growing medium, net pots, water, an air pump and stone, and a growing tray.

What Is The Best Hydroponic System For Onions?

Indoor Growing Space

Hydroponics set-ups are usually set up inside or in a greenhouse. Setting up your growing environment will be relatively similar, but you will need lighting for an indoor environment whereas this might not be necessary in a greenhouse.

What Is The Best Hydroponic System For Onions?

You can use either a flood and drain (ebb and flow) or DWC (deep water culture) system to grow your onions. It’s up to you to decide which hydroponics style you are most comfortable with.

A deep water culture system is beginner-friendly and will use an air pump to distribute oxygen to your nutrient solution.

Your plants will be secured by plastic or styrofoam and suspended over the water. It’s great for small spaces.

DWC will allow you to use separate grow trays or containers so that you might have a reduced risk of roots tangling up with each other or becoming diseased.

For root crops like onions, this can be quite advantageous. Ebb and flow is another great option. It will flood your plants with nutrient solution, then slowly drain it back out to reuse it later on.

It’s best for plants that need prolonged periods of dryness and can also work well with root crops like onions.

Consider Building Your Own System For Hydroponic Onions

You can buy a system online or you can build one yourself. Building a hydroponics system can be somewhat complicated, but definitely not out of the question if you want to save some money and are relatively handy.

Consider Building Your Own System For Hydroponic Onions

If you decide to do this, you’ll need, at a bare minimum, the following equipment:

  • Grow tray and stand
  • Air pump and air stone for oxygenating the nutrient solution
  • A resource to hold the nutrient solution
  • A water pump to get the solution from the reservoir into the grow tray, where your plants will be “rooted”.
  • Hydroponic tubing
  • Net cups

As you can see, there’s a lot that goes into building a hydroponics setup - so in many cases, you may find it easier to purchase a system from Hydrobuilder’s hydroponics section and get the whole thing done at once.

Hydroponic Grow Media & Nutrients

No matter which of these systems you select and regardless of whether you purchase a premade unit or build one yourself, you’ll also need growing media and nutrients.

Onions are relatively easy going when it comes to their nutrient needs - they don’t need a lot of fertilizer.

However, you can supercharge their growth by adding some nutrients. Nitrogen, for example, is essential - although you want to avoid adding too much as it will create lush foliage rather than bulbs.

If you add fertilizers, do this later on in your growing cycle rather than at the beginning, as it can stunt the growth of seedlings by burning them.

As for growing mediums, there are several options you can choose from. You can use composite plugs, rockwool, or perlite.

How To Actually Grow Hydroponic Onions

Before you can start growing onions hydroponically, you need to first decide which seeds you’d like to start.

Many people grow green onions in this kind of setup since they grow quickly, though they’re much smaller than regular onions.

The instructions below will tell you how to start growing hydroponic onions in a deep water culture method, since this is one of the most common ways to grow hydroponic onions.

Prepare Your System & Net Pots

Start by filling your net pots with your growing medium (like perlite). Net pots have holes in the bottom and are designed to be used in a hydroponic system so that nutrients can get to the plants’ roots with ease.

These pots also make it easier for the solution to drain. We recommend using three-inch net pots for this type of vegetable. Insert each onion halfway into the medium, then insert your pots into the grow tray.

Let it fill with water before you add your air stone. This will add oxygen to the system. Add your air pump, which will push the oxygen where it needs to go.

Start Your Onion Bulbs Or Seeds

When you plant your bulbs, try to do so at roughly the same height. Then, when you add water, you won’t have to worry about dampening the bulbs and causing rot.

Start Your Onion Bulbs Or Seeds

At the same time, though, your roots will be adequately moistened. You can also start your onions from seeds rather than from bulbs or sets, although this will admittedly take a bit longer. It will take around 10 days for your seeds to germinate.

We recommend starting the seeds on a sunny windowsill or under a grow light. Plant the seeds about ⅓” deep and about ¼” apart.

You can transplant into the net pots after around 30 days. Hydroponic onions do best in full sun, so if you’re using a hydroponic system indoors, you will want to give them about 12 hours of light per day via your grow lights.

Maintaining The Environment & Hydroponic System

The temperature should remain at around 55 to 75 degrees Fahrenheit. Once your onions are planted, you won’t have to do much to care for them.

Maintaining The Environment & Hydroponic System

Check your nutrient solution on a regular basis, making sure the pH remains at around 5.5 to 7.0.

You shouldn’t need to fertilize often, but if you do, use a balanced nutrient solution that is designed specifically for root vegetables.

The water you use in your system should be unchlorinated, but if you must use chlorinated water, just let it sit out for 72 hours so the chemical dissipates.

When you add nutrients to your reservoir, wait an hour, then check the pH to see if it needs to be adjusted.

Finally, make sure your hydroponic onions have access to good air circulation. Otherwise, they can become rotted and mildewy.

How To Harvest Hydroponic Onions

While green onion tops can be harvested in as little as three weeks from planting sets, you will need 80 to 90 days to harvest bulb onions.

How To Harvest Hydroponic Onions

The best time to harvest hydroponic onions is first thing in the morning. Harvesting these is not dissimilar to harvesting onions that you grew in a traditional garden.

Simply pull them up and they’re ready to use. If you see any flower stalks emerging from the onions, that’s a good sign that the onions have stopped growing and are ready to be harvested.

Another good indicator that your onions have matured is that the foliage has turned yellow and tipped over. After harvesting your onions, let them dry to cure.

To do this, lay them out on a flat surface with good air circulation and cool temperatures. Store them in a crate or in an old onion sack out of direct sunlight and they should last for several months.

Final Thoughts On Hydroponic Onions

Hydroponic growing may have a bit of a learning curve, but once you get the hang of it, you’ll find that your yields and productivity are dramatically increased.

Hydroponics onions are not only tasty and nutritious, but they’re also some of the easiest hydroponic vegetables to grow.

If you follow our guide on growing onions hydroponically, you'll be well on your way to cultivating delicious, clean food!

You can also shop for all of your hydroponic supplies at Hydrobuilder. The time has never been better to start your own indoor hydroponics system, so what are you waiting for?

Have questions about your grow? We're Here To Help!

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