Simple Hydroponics – How to put together a simple Kratky system

Our Kratky System

I want to keep this short  – so if you’re curious about how things went for us, here’s some photographic evidence of how things are going so far!

Off to a good start!
Into the system they go
2 weeks later…
Hard to believe that we were able to pick this much 3 weeks after being in the system
After picking – still enough for another salad!

How to Build Your Own System

Note – This method works well for leafy greens (we’re growing kale, bok choy, lettuce, arugula, basil and cilantro). Flowering/fruiting plants will not do as well due to the higher water and nutrient demands of flowering/fruiting. 

Here’s a quick list of the items needed to get set up.

Starting The Seeds

    1. In a big bowl or small bucket, fill it with enough tap water to soak however many rockwool cubes you’ll be putting into your system.

    2. Check the pH of your tap water using a pH meter or a pH sample kit. If you have really hard tap water ( >8pH), you may want to consider dropping the pH a bit to no lower than a pH of 5.5. Our tap water sits at around 7.5pH and we didn’t have trouble with germinating (other reasons caused trouble which I’ll mention later).

    3. Break off the amount of rockwool cubes you’ll need to plant your seeds in. Soak the rockwool in tap water for 5 minutes. When taking the rockwool out, do not squeeze the extra water out. Let the excess water drip until it stops on its own.

    4. Place the soaked rockwool into the seed starter greenhouse tray. Drop in 2-3 seeds of your selected veggie into each cube. If you’re pretty confident in your seeds germinating, you can put in less. Make sure the seeds are at least slightly below the top of the rockwool.

    5. Depending on what kind of veggies you’re sprouting, you’ll need to create the right climate for them to germinate. Starting out, you’ll want to place them in a dark spot. The part that takes a little bit of research at what temperatures will the seed germinate.As I mentioned above about germination troubles, our cilantro wouldn’t sprout when it was on the heat mat. We thought it was just some bad seeds. However, when we moved the other veggies out and let the cilantro seeds sit with the heat mat turned off,  they ended up sprouting a few days later!

    6. In, what should be, less than a week, sprouts should be coming up! When majority of the veggies have sprouted, be sure to put them under your grow light. If they stay in the dark too long, they may get overly leggy.

Note – The grow light should be around a foot and a half above the top canopy of your plants.  Keep an eye out for leaf scorch which means your lights are too close to the canopy. If your veggies are getting leggy, the light is too far away. 

Occasionally douse the surroundings of your rockwool with very diluted (1/4 part nutrients to 1 gallon of distilled water) water to  keep the rockwool wet.

Modifying the Tub

You’ll be placing the net cups which hold your plants on the lid of the tub. Make sure that your plants have ample space to grow! Our current system is a bit crowded (3 rows; 4 columns), but we still get good yield and the plants are able to grow well from what we can tell!

Drill out as many slots as you’d like using the 2″ hole saw. Check to see that the rim of your net cups sit comfortably in the lid. You’ll want to make sure that no light can get in from around the rim of the net cup! Later on once your plants are in the system, some form of opaque tape works well (electrical tape for instance) to seal things up.

Making the Nutrient Solution

You’ll know it is time to move your seedlings into the tub once you start to see tiny little white roots shooting out the bottom of the rockwool. Once that occurs, you’ll want to get the tub filled up with nutrient solution.

You’ll want to add in enough water so just a little bit of the bottom part of the rockwool (where the new roots are) will be sitting in the nutrient solution. Try placing some net cups in the system to see if the water is high enough to submerge the bottom part of the net cup. Adjust as necessary.

For the Flora series nutrient solutions, they provide a dosing table on the bottle. We went with somewhere in between “General Purpose – Mild Vegetative” and “Aggressive Vegetative Growth”. Last thing we wanted was to cause nutrient burn to our seedlings but we also wanted to see how fast this system could grow veggies.  So far, we haven’t had any issues!

We recommend that when mixing your nutrient solution for your system that you add in the nutrients first before balancing the pH. Nutrients tend to drop you pH. We ended up not having to do any pH balancing since the nutrients brought it down to just the right levels. 

Balance your nutrient solution to between 5.5pH and 6.5pH. If the solution is too acidic/basic, nutrient lockout can occur.

Check out this video from General Hydroponics on how they recommend to mix the solution together to create your nutrient mix.

Moving to Their New Home

With the nutrient solution all mixed together and pH balanced, place the seedlings into the net cups. Keep the top of the rockwool level with the top of the net cup.

One thing that we ended up doing to further make sure that light wouldn’t get into the nutrient solution was to tease apart the rockwool plugs a bit. We ended up sacrificing a rockwool cube to help fill some of the gaps by tearing it apart and placing it where gaps occurred. This made sure that no empty space was left for light to pass through.

That’s it! All that’s left is to turn on and off the light. Make sure that your plants get 14-16 hours of light!

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