How to: Grow Hydroponic Kale

By: Chris | Last Updated: November 3, 2020

In 2016, a foodie film called “Suicide Kale” earned accolades for its relationship insight. Over dinner conversation, four women talk about how they serve their partner’s favorite foods to form a psychological connection between the taste buds and their romance.

The strategy is darkly dysfunctional because it’s really about creating a post-breakup association. The other person will never be able to eat the food again without thinking about them. Yikes! One brings home blueberries, the other mint chocolate chip ice cream, none bring home kale. What the lovers failed to realize is that kale delivers a massive nutrient dose that balances your hormones and enhances the libido.

If you want to make kale a fast food, you can quickly harvest for salads, sandwiches, or use as a psychological relationship weapon, this is how to grow hydroponic kale.

Fun Facts About Hydroponic Kale

National Kale Day falls on the first Wednesday of October. The Germans hold an annual celebration called Grühnkohlfahrt, and people fill their plates with kale and drink beer. We all know what happens after stoking the libido with alcohol and kale.

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One last fun fact, the traditional Netherlands dish — stamppot boerenkool — blends kale with mash potatoes. Comfort kale?

Hydroponic Kale in Rockwool

How to Grow Kale Hydroponically 

Even if you are not sold on kale being the building block of a dysfunctional relationship, the health benefits are not an urban legend. By learning how to grow hydronic kale, you’ll have a readily available leafy green whenever you’re in the mood. This is a step-by-step DIY method that allows you to grow a robust harvest or modest window garden without heightened gardening experience.

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How to Set Up Hydroponic Kale

  1. Mix the distilled water with the recommended hydroponic nutrient solution.
  2. Soak Rockwool cubes or other seed starting plugs (Rapid Rooter) in solution.
  3. Place 1-3 kale seeds in each growing cube. If more than one plant successfully spouts, you may need to thin later.
  4. Place net pots into the neck of a mason jar or suitable liquid nutrient container.
  5. Place Rockwool Cubes into net pots.
  6. Cover with plastic wrap to create a greenhouse effect.
  7. Net pots must remain slightly below the liquid nutrient level to ensure consistent wicking.
  8. Once the seed sprouts, allow it to develop for a few days before removing the plastic wrap.
Hydroponic Kale Fact Sheet

Pro Tips on How to Grow Hydroponic Kale

As you can see, the average DIYer can setup a kale-growing system. But the difference between a terrific yield and skinny kale typically comes down to knowing insider tips. These are a few that support hydroponic success.

Harvested Hydroponic Kale

How to Harvest Kale Without Killing the Plant 

In all likelihood, you can begin harvesting baby kale at about 30 days. To fully mature, a kale plant will take 60 to 90 days. In terms of kale yield per plant, the amount of leafy greens you enjoy has a great deal to do with your harvesting methods.

If you strategically harvest leaves from the plant’s sides, it generally continues to grow and flourish. Clipping kale from the top usually stunts its growth.

Pick & Come Again Tips

To harvest a kale leaf, grab an outer leaf down at its base, pull down and outward and the leaf should snap off easily. If you’re harvesting a younger plant you may prefer to use a knife or scissors to keep from accidently snapping the main stalk of the plant.

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Pick and come again harvesting will provide multiple harvests as your hydroponic kale will continue producing. To keep the plant healthy, only harvest outer leaves and always leave at least 4 to 5 inner leaves growing until you’re ready to completely harvest and remove the plant.

Harvesting Kale Seeds

How to Harvest Kale Seeds

If you are wondering, does kale bolt? The answer is a firm: Yes.

If you plan to harvest kale seeds, you need to start with a good Non-GMO heirloom seed, like these Dwarf Siberian kale seeds.

Kale seeds are inexpensive. Bolting kale takes up a lot of space in a hydroponic garden, often growing too tall to fit under grow lights. Also keep in mind that leaves from a bolting plant are often too bitter to be of any use.

Bolting Kale
As kale begins to bolt, flowering stalks will rise up from each plant. These stalks will grow anywhere from 3 to 5 feet tall. Remember that part about growing too tall to fit under grow lights?

Once the flowers bloom and drop, long seed pods will form. They look very similar to pea pods. Once the pods begin to fade from bright green to yellow, cut the stalks. If you wait too long, the pods will open and begin dropping seeds.

Place the cut stalks in a paper back with the cut ends sticking out the top. Tie the top of the bag around the stalks with twine, and hang them up to dry. When hanging the stalks, choose a place that is cool, dry, and out of the wind or direct sunlight.

Note: No more than 3 stalks should be bundled together. This will help reduce humidity in the back, and limit the risk of mold growth. Avoid plastic bags since they trap moisture.

It takes 10 to 20 days for the seed pods to dry completely. To test dryness, hold the bag by the twine and slap the stems lightly. If you hear pods breaking and dropping seeds, the stems and pods are dry. To dislodge the seeds from the pods, shake the bag and continue to lightly slap the stems.

Once you’ve given your stems a good beating and dislodged all the seeds, it’s time to separate the seeds from the chaff (stems, casings, etc). Kale seeds will be any combination of black, tan, or gray. The easiest way to separate, or winnow, seeds from chaff is with a properly sized screen. This screen will allow seeds to fall through, and traps chaff on the screen.

If you don’t have a screen, you’ll be manually separating seeds. It’s a tedious job, but you’ll have those precious seeds you’ve been wanting!


How long does kale take to grow?

30-60 days. Baby kale will normally be ready to harvest at 30 days, and it will take around 60 days for kale to be fully mature. You do not have to wait until the plant has fully matured in order to harvest leaves.

How much space does kale need to grow?

Kale can grow well in relatively tight quarters, with rows needing only about 6 inches of spacing between plants. Plants normally grow and thrive much closer to each other in a hydroponic system thanks to the abundance of nutrients and direct overhead lighting.

How deep does a container have to be grow kale?

In a hydroponic system, kale will grow well in containers as shallow as 3 inches. As long as there is enough room that the roots don’t bind and clog the system, the plant will thrive.

What temperature to grow kale indoors?

An Air temperature of 75-82°F and water temperature ranging between 65-70°F is the optimal temperature zone for growing kale indoors.

Time to Grow

The good news is that growing kale indoors in a hydroponic garden produces very well. The bad news is that no matter how many times you serve your love-interest kale salad, they will keep on eating it after putting you in their rearview mirror. It’s healthy, but not as sexy as blueberries or ice cream.  

Chris Cook started Happy Hydro Farm to share his passion for hydroponic gardening! Growing your own food is incredibly rewarding both physically and mentally. His mantra - "Take excellent care of your plants, and your plants will take excellent care of you."