Hydroponic Onions

Hydroponic Onions – The Ultimate Guide

Growing your own vegetables is a gratifying process that not only satisfies you but also proves to be a job that requires the utmost care and responsibility. And really, when you grow groceries yourself, they somehow taste even better. One of the most important among the many kitchen requirements is onions. And an interesting thing about it is that you can even grow in hydroponically! Now, it may seem like a process that is time – consuming and complex but if you know the right things to do then growing hydroponic onions will turn out to be very interesting.

For the purpose of recollection, Hydroponics is where you grow plants without the aid of soil, by only growing them in nutrient water or moist air. And you, hydroponically, would be cultivating onions. And don’t worry if you think this is a mountainous task, because even if it is, we’re here to make it easier for you.

Hydroponically, onions are one of the easiest plants to cultivate. For a beginner too, staring with onion would not be a problem at all because it really is that easy to hydroponically grow onions. So how do you grow hydroponic onion? Simply, it’s the process as detailed below.

A simple process To Grow Hydroponic Onions

Let’s begin with the process that’s required to set up the hydroponic system to begin growing the onions.

  • First, you have to decide upon the spot where you’ll [lace your set – up. With onions, you can either grow them indoors or outdoors so depending upon what’s feasible for you, you can place your set – up where ever.
  • The onions can either be grown directly from the stage of seeds or you can plant bulbs first. Using small onions bulbs and then placing them in a growing containing medium outside the hydroponic set – up can be an easy way for you to go about it. So first, you plant the bulbs, let them grow to a certain stage and then you ever so slightly insert them into the hydroponic set – up. This is so that the plant reaches a stable stage and can easily adjust into the hydroponic set – up with strength and presents no hassle in doing so.
  • The growing medium for your plant is a very important aspect. Media such as composite plugs or Rockwool or even just plain old soil will do when you first plant your small onion bulbs. Once they grow a little, they can then be inserted into the Hydroponic system.
  • Now, the type of growing media you are using is of no concern in the way you would grow the initial onions. Place your seeds or bulbs in their respective growing media. 
  • In order to irrigate them, you can use one of three methods: onions seeds are tiny. So you can either soak them in the water for a while or you can wet the seeds or you can just simply place the seeds in their growing media and then sprinkle water on top of them. Remember because the seeds are tiny, they can easily be washed away if there is more force.
  • Now moving on to taking care of them, new onions seeds do not require any nutrients. In fact, nutrients can also prove to be harmful to them. This is because the embryos in the seeds already have the nutrients and energy required by the seed to grow and this is what is used by the seed. So adding more artificial nutrients, would harm the plant.
  • A big no also to using fertilizers. The seedlings do not need fertilizers. They can harm the seedling by chemically burning them or stunting their growth. Such a thing can also ultimately lead to the plant’s death. The seed has the requirements necessary for it to develop into a seedling which is why no outside input is necessary at all. All you have to do is supervise and irrigate.
  • Place these little cultivated seeds in a dark and warm place for them to grow well.
  • Once they’ve begun sprouting into tiny plants, transfer them with their growing media into the Hydroponic set – up.
  • While setting up your water reservoir, which you can easily make by yourself with simple items, make sure it is at least 6 – 8 inches deep. 

After we’re done setting up the seeds for the hydroponic system and the hydroponic set – up is ready, it is now time to begin using it for its purpose. There are some steps that you need to follow to be able to grow healthy hydroponic onions.

The onion seeds will take a duration of about 6 – 10 days to germinate at an ideal temperature of 65 – 70 F.


The water reservoir requires nutrients essentially, yes, but for onions, it’s better to starve them during the initial stages, when the seedlings are growing. This is so that the roots are able to grow longer in search of nutrients and stronger during the search. They will strengthen themselves and later when you add nutrients, they will use them with their strong roots. This helps establish a strong roots base for the plants and will increase growth. Use a nutrient solution that is targeted for root vegetable growth.

The balancing of nutrients may be tricky for onions. Nitrogen is essential to the plant. But adding too much of it will neglect the onion bulbs for the benefit of the foliage. And too little nitrogen will reduce the plant stamina and growth. The supplying of proper nutrients is also characterized by supervising the pH levels and electrical conductivity.

The nutrient solution must be changed once every three weeks.

pH Levels

It is important to maintain the pH levels of the water reservoir for the well growth of the onions. Add the nutrients to the water and then check the pH levels after an hour. 5.5 to 6.5 is the preferred levels for optimal growth. Keep monitoring the levels throughout or else the plants might get damaged.

Chlorinated water

Chlorinated water is not recommended but if you are using it, then the chlorine has to be erased from it before use. This can be done by allowing the water to sit for an hour or so before the chlorine dissipates. You can then put the water to use in your hydroponics system.

Light supply

Onions require full sunlight in order to cultivate properly. They need a minimum of 12 hours of light for health. In case you are placing your hydroponics indoors, then you have to make arrangements to see to it that they receive adequate sunlight at all times. Otherwise, all your efforts will go to waste as the plants will deteriorate without light. 


Onions thrive in a temperature between 65 – 70 F. Providing the plants with such a temperature will help boost growth and allow for healthier plants. The plants growing outside such temperature range will not grow optimally as desired.

No matter how well you cultivate your plants and what level of machinery or products you use, if you don’t care about protecting your plants from pests well enough, then it all goes down the drain. So here are a few things to look into:

Air circulation

It is very important, especially for hydroponic plants. Because they grow in high levels of moisture, if air around them is not circulated properly, then it may lead to the growth of mildew or bacteria. And this can prove detrimental to your plants. To have a good air circulation you can install exhaust fans or floor fans or ceiling fans, or even keep a window open. But whatever you do, make sure to see that there is good ventilation.


Aeration of the nutrient solution is also imperative. This will allow the retaining of the nutrients for a longer time and will also prevent anaerobic bacteria from attacking the plants. The roots will be oxygenated which will help in the better growth of the bulb.

Onions are plants that can easily tolerate cold conditions and get through frost and snow. However, in a hydroponics set – up, you also have your nutrient water solution. So if you place your hydroponics outside in the cold, then there are high chances of your water solution freezing. If the temperature is not between 55 and 75 F then the onions will bolt to seeds. Such onions must immediately be harvested.

Damp conditions often lead to the growth of algae. You have to be very careful with hydroponic setups because they can easily facilitate algae growth if they are under direct sunlight. Use a shade over your plants to avoid such a scenario.

It is important to look out for mildew that can be caused by water. This can be avoided if you religiously sterilize and thoroughly clean all your equipment that comes in contact with water. Any 2% bleach concoction will get the work done. 

You’ve put in the work, and now your lettuce is ready to harvest. That too requires a careful but simple process.

If you’ve begun your onions from seeds, then harvesting will occur after 3 – 4 months. And if you’ve begun with small bulbs, then expect the plants to be harvested within 80 – 90 days.

  • Harvesting hydroponic onions are not very different from harvesting conventionally grown onions. It’s the same rooting process that you have to follow.
  • If there are flower stalks emerging from any onions, that means they have stopped growing and need to be pulled out.
  • When the foliage yellows and falls over, it means they are in the last stage of ripening and can soon be harvested. 
  • The soil around the bulbs can be loosened for drying and once the foliage is brown, pull them out.
  • Dry the onions after pulling them out and only after they’re dried can you store them in a dry and cool place.
  • Pungent onions store longer and sweet onions last comparatively less. So use up the sweet ones first.

And that’s it, folks! That is the process for you to follow in order to grow healthy, fresh and tasty onions hydroponically.

Reading through this process, you’ll have made the decision for yourselves: hydroponic onions are easy to grow and require little effort and a little investment. So little for so much more. And in the end, you will be left wanting more.

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