Nutrient Guide: How to Grow Onions Hydroponically


Growing crops through hydroponics is all the rage nowadays, and a large variety of fruits and vegetables can be easily grown via hydroponics. Today, we are going to focus on a kitchen staple – onions. 

For those unfamiliar with the concept of hydroponics, it is the act of cultivating plants with simply nutrient water or moist air, without the conventional soil. Although this process may sound pretty overwhelming and complicated, it is actually pretty handy and manageable once you have gotten the hang of it. Don’t worry, we’ve got your back and put together a foolproof guide, so read on if you are ready to try something new and different.

Setting up the hydroponic system

Before we dive into the cultivating part, we need to make some preparations and the setting up of the hydroponic system in which the plants will be growing in. Choose a spot in your home to place the setup. Thankfully for onions, both indoors and outdoors will work fine, so don’t fret if you don’t have access to a yard or an area specifically for gardening. 

Next, you have to procure onion bulbs to kickstart the hydroponics process. The common way of going about obtaining these is to plant onion bulbs and allow them to grow till a stage where they look sturdy enough and ready to be switched into the hydroponic setup. Growing the onions from seeds will work as well. Let’s take a closer look at how we can achieve these hydroponic-ready onions.

The growing medium will be the next important thing for you to consider. We suggest medium including composite plugs, Rockwool, and plain old soil. Concerning irrigation, we would recommend soaking the seeds in water or wetting the seeds. Otherwise, sprinkling water after the seeds are placed in the growing medium is fine too.

A misconception many have is that these seeds require additional nutrients and fertilizers. They absolutely do not need them to grow healthily. Conversely, introducing these substances may actually impede the growth of these plants and even hurt them. The worst-case scenario is that your plants may die. Simply irrigating and closely monitoring the plant is more than enough.

For the best results, placing these seeds in dark and warm places is recommended. The moment the seeds germinate and sprout into tiny plants, they are ready to go in the hydroponic setup, together with their growing medium. 

Follow these guidelines and you can prepare for the onions seeds to start sprouting at about six to 10 days maximum at an optimal temperature of 65 to 70 F.

Now, before we get into the actual cultivation of the onions, an important thing to note is to ensure that the water reservoir of your hydroponic system is more than six inches deep. 

Hydroponic Onions’ Growing Requirements

Onions Farmers Market

There are several conditions that you need to take note of to cultivate healthy onion plants. For starters, the nutrient mix for onions. Typically for onions, it is highly recommended to starve these plants at the start as growing seedlings, which allows for longer roots and an overall stronger plant. The nutrient solution that you ultimately want to use is one that is suited for root vegetable growth. 

Here’s the tricky part. The nutrients for onions have to be balanced appropriately, especially nitrogen. Too little of this nutrient and it will impede the plant’s growth and stamina, but an excess of it prevents the onion bulb from reaching its maximum growth potential. Before we give our recommendations on the pH levels, you should also remember to change the nutrient solution every three weeks.

The pH levels of the water reservoirs have to be monitored closely for the optimal growth of the onions. The recommended range is between 5.5 and 6.5.

What’s more important is the aeration of the nutrition solution. A well-aerated solution will aid in the growth of the bulb. Keep an eye on the solution as well, and avoid situations that will cause the nutrient solution to freeze under or an infestation of algae and mildew. Consider adopting proper sterilization practices of the pieces of equipment utilized.    

The light requirement for onions is complete sunshine for at least 12 hours. Those with their hydroponic setups indoors should ensure that sun rays hit the plants.

Air circulation should also be a factor to look out for. Areas with poor air circulation that are prone to mildew or bacteria growth are absolutely harmful to the growth of your plants. As such, do your best to keep some airflow going in the space you place your hydroponics systems and plants.  

As mentioned, the optimal temperature for onions is between 65 to 70 F. While onions can grow outside this range, they will not be at their best. One last thing is to avoid the use of chlorinated water. You can eliminate traces of chlorine by letting the water sit out for an hour before using it in your hydroponics system. 

Now that we have gotten the details down, expect the onions to be ready for harvest in three to four months for seeds and 80 to 90 days for small bulbs. Although harvesting hydroponic onions are rather similar to conventionally grown onions, here are some harvesting facts that will serve you well to know.

Keep a watchful eye on yellow and falling foliage, as they are signs that the onions are going to be ready for harvest very soon. Emerging flower stalks from onions are indications that they have ceased growing and need to be pulled out. Browned foliage means that you can now pull the onions out. Remember to dry the freshly harvested onions before storing them. Sweet onions also do not last as long as the pungent ones, so keep this in mind when planning for meals. 

In conclusion


Hydroponic onions are not that tough to cultivate as one would imagine. In fact, they are pretty easy to work with, and the satisfaction of harvesting your homegrown hydroponics onions is not something that one can experience simply by buying the usual onions at the local groceries. Once you have mastered cultivating hydroponic onions, you will be well prepared to try your green thumb at other kitchen essential plants. 


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