A Simple Spin on Kratky Hydroponics

The next adventure in growing our own food starts today. We’re going to try Kratky Hydroponics. This is similar to the Deep Water Culture Hydroponics we did in a previous post (here) but without the air stone and air pump. Normally you would still use the net cups and rapid rooter starter plugs but we’re going to try to simplify things even more.

For this experiment I’ll be using 5 supplies I purchased. The rest will be from around my house. We’ll be purchasing:

The optional supplies above will help your lettuce grow faster, but you might be able to get by without them. If I was to pick one or the other to buy, I’d go with the PH Control Kit. I’ve had problems with the plants not getting the nutrients they need when my nutrients were at the wrong PH. With distilled or RO filtered water, you’re less likely to need to adjust the PH. The other supplies I’ll use that I had laying around the house:

  • A plastic bottle
  • Utility Knife
  • Drill and Drill Bit (optional)
  • Flush Cutters (optional)
  • Aluminum Foil/Spray Paint/Non-Transparent Bottle

Kratky hydroponics is pretty neat. It requires less maintenance than the deep water culture when used with crops like lettuce because you only fill the container once. As the plant grows it uses the nutrient solution and by the time it runs out you’ve harvested the plant. Instead of delivering oxygen to the roots by an airstone, and oxygen zone is created as the plant uses the nutrient solution and a space forms between the netcup and the water level.

Here’s how I set this up.

I took my plastic bottle (make sure you’re using type 1, 2 or 5 plastic) which was an old popcorn container and rinsed it out with water. I then drilled holes in the cap for the water to get to the growing medium and for the roots to grow through to the nutrient solution.

Drilling the first hole in the cap of the bottle
Drilling the first hole in the cap of the bottle
Picture of the finished product after drilling holes in the cap
I drilled a series of holes in the cap

After this I used some flush cutters to clean up the inside on the cap since the process of drilling it tends to melt the plastic. If you don’t have a drill and drill bits available, you might be able to just use a knife to poke holes in the cap. Be careful though!

Next I drilled another series of holes into the side of the bottle towards the top to allow for additional drainage and hopefully for the roots to grow through.

Picture of hole being drilling in the top section towards the top of the bottle
I drilled another set of holes towards the top of the bottle
A ring of holes around the side towards the top of the bottle
You can see a ring of holes drilled in the side of the bottle. I started by drilling holes across each other and then kept filling them in by drilling holes in the middle of the previous ones.

Now for the fun part. We need to flip this top part of the bottle around so it sits on top of the rest of the bottle. This particular bottle’s design is really convenient for this. The bottle widens below the cap, then narrows before widening again to the diameter of the rest of the bottle. I’ll cut through the ridge before the narrow section and it’ll sit on top.

Bottle being cut with utility knife
I use a utility knife to cut the top off the bottle. You might get a more even cut by using a larger kitchen knife. Be careful with this step!
Top section of bottle with cap sitting on bottom part of bottle
Finished product of the top of the bottle sitting on the bottom

We’re almost there! After rinsing out the bottle from all the plastic shavings, the last thing we need to do is protect the roots from light. I used aluminum foil, but you could also spray paint the bottom of the bottle. If this setup is going outside you might want to paint it white. If it’s inside, it should be fine to paint it black. We don’t want the roots to get too warm, so sometimes it’s helpful to paint it white. I wrapped the aluminum foil around the bottom of the bottle.

Foil lined up on bottle to be wrapped around
I wrap the aluminum foil around the bottle leaving a little extra on top that I can use to push over the top edge of the bottle.
Inside of Bottle with Foil Wrapped Around
Here’s the inside of the bottle after the wrapping the foil around.
Outside of Bottle With Foil
Here’s the outside of the bottle with the foil wrapped around

That should protect those roots! This also creates a handy place to label you’re container with a sharpie so you can remember what you plant and the date.

I’m starting the seeds directly in perlite this time around partly as an experiment and partly because I still have a bunch of plants growing in my seed starter tray from a month ago. This method may not work. I’m not sure if the perlite will stay moist enough to trigger germination so the seeds can sprout and I’m not sure if it will be stable enough for the roots to grow through but I’m hoping it’ll work and I’ll keep you updated with the progress. You could definitely use the net cups. Or, even without netcups you could still use rapid rooters and fill in the top with clay balls to keep it steady.

Bag of perlite sitting behind the top section of the bottle
I used this Perlite I got from Amazon to fill the top

Now it was time to fill up the bottom of the container with nutrient solution. I used the leftovers of some nutrient solution I mixed up a few days ago in a one gallon water jug. There’s around 1-1.5 teaspoons of Maxigro and 1 teaspoon of CALiMAGic. I’m starting with a full dose of nutrient solution since I should be able to let the plant grow to harvest without changing the reservoir. Generally you want to slowly increase the nutrient concentration as the plant grows so this is another experiment in the process.

I checked the PH of the nutrient solution to get it between 5.5 and 6.5.

And added a little more nutrient solution until the cap was a little submerged in the nutrient solution. I figured it would help keep the perlite somewhat moist and the roots would find the nutrients quicker than if they had to grow down through the cap.

With the water level set, I put the foil back in place and planted the seeds. I went with buttercrunch lettuce that I picked up from the local hardware store. In theory, I should be able to get a harvest in a little over a month.

I generally plant a few seeds at a time in case some of them don’t sprout. If more than one happen to sprout I can either cut away the ones I don’t want, or carefully pull them out and transplant them somewhere else.

I made a little hole in the middle, place the seeds inside and covered them up.

Finally I covered the top of the container with a plastic sandwich bag to act as a humidity dome. While the seeds are sprouting you want to keep the environment humid to encourage germination of the seeds. As soon as your see leaves come through the bag can be removed.

I put the container near my grow lights so as soon as the seeds sprout they’ll get plenty of light. I’ve made the mistake in the past of starting seeds in a room that didn’t get much light and they tend to grow tall and thin (“leggy”) which causes them to have a hard time staying upright once they get leaves. Hopefully having the seeds near the lights from the start avoids that.

That’s all there is to it! I’ll keep you guys up to date on how things progress with this experiment of mine! This is my first time trying the Kratky method so I’m hoping to get a good harvest out of it.

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